IRLF 


ELECTRIC 


PAGET   HIGGS.  LL.D. 


GIFT   OF 


ELECTRIC  TRANSMISSION  OF  POWER. 


ELECTRIC  TRANSMISSION  OF  POWER 


ITS  PRESENT  POSITION  AND 
ADVANTAGES. 


BY  PAGET  HIGGS,  LL.D.,  D.Sc., 

TELFOKD  PRIZEMAN   AND  ASSOCIATE  OF   THE  INSTITUTION   OF  CIVIL 

ENGINEERS ; 

AUTHOR  OF    '  THE   ELECTRIC   LIGHT   IN   ITS  PRACTICAL   APPLICATIONS,'    '  ELECTRIC 
LIGHTING,'  '  ELECTRICAL  FORMULA  '  (MOLESWORTH),  ETC. 


LONDON : 

E.  &  F.  N.  SPON,  46,  CHAEING  CEOSS. 

NEW  YOEK:  446,  BEOOME  STEEET. 

1879. 

J,  C.  Cebrian, 


PEEFACE. 


IT  is  needless  to  dwell  upon  the  benefits  of  economical 
transmission  of  power.  Where  distance  is  involved,  none 
of  the  existing  systems  are  so  nearly  perfect  as  to  leave 
no  room  for  fresh  trials ;  on  the  contrary,  all  kinds  of 
manufactures  and  trades  are  alive  to  a  simple  means  of 
transmitting  power. 

Extensive  experience  with  dynamo-electric  machines 
and  their  various  uses  has  shown  me  that  electric  trans- 
mission has  before  it  a  very  wide  field.  For  this  reason, 
I  have  collected  into  the  following  pages  the  most  re- 
liable data  on  this  subject,  and  have  added  some  experi- 
mental results  from  my  own  working.  I  hope  I  have 
furnished  to  the  inquirer  that  information  which  will 
enable  him  to  form  his  own  opinion.  It  may  be  well  to 
point  out  that  I  do  not  propose  a  system  of  my  own  nor 
advocate  specially. 

First  describing  the  machines  employed,  their  relative 
merits  and  demerits,  there  is  next  considered  the  me- 
chanical ratio  of  the  efficiency  of  this  method  of  trans- 
mission, and  its  applicability  either  to  short  or  long 

249962 


VI  PREFACE. 

distances.  Some  objections  that  have  been  advanced  are 
met,  and  in  conclusion  are  given  some  of  the  most 
definite  advantages  of  employing  electricity. 

I  hope  that  the  desire  to  afford  information  upon  a 
comparatively  novel  subject  may  be  taken  in  palliation  of 
shortcomings  in  style  and  arrangement. 

PAGET  HIGGS. 


CONTENTS. 


CHAPTER  I. 

PAGE 

DYNAMO-ELECTRIC  MACHINES     1 


CHAPTER  II. 
THE  GRAMME  MACHINE       


CHAPTER  III. 
THE  BRUSH  MACHINE 11 

CHAPTER  IV. 

THE  WALLACE-FARMER  AND  SIEMENS  MACHINES 19 

CHAPTER  V. 

EFFICIENCY  OP  DYNAMO-ELECTRIC  MACHINES 24 

CHAPTER  VI. 

PRACTICABILITY  OF  TRANSMISSION  OF  POWER  BY  ELECTRICITY    .      34 


yiii  CONTENTS. 

CHAPTER  VII. 

PAGE 

EFFICIENCY  OF  COUPLED  MACHINES 47 

CHAPTER  VIII. 

COMPARATIVE  EFFICIENCY  or  VARIOUS  MACHINES 59 

CHAPTER  IX. 

OTHER  THEORETICAL  CONSIDERATIONS      78 

CHAPTER  X. 

CONCLUSIONS 85 


ELECTEIC  TRANSMISSION  OF  POWER. 


CHAPTER  I. 

DYNAMO-ELECTRIC   MACHINES. 

WITHOUT  the  invention  of  the  dynamo-electric  machine, 
transmission  of  power  by  electricity  could  never  have 
become  an  accomplished  fact.  But  the  growth  of  elec- 
trical invention  has  been  so  rapid  that  it  may  be  de- 
sirable to  indicate  what  is  meant  by  a  dynamo-electric 
machine,  and  advisable  briefly  to  review  this  branch  of 
electricity. 

The  principles  of  magneto-electricity  were  elucidated 
by  Faraday,  who  found  that  when  a  bar  of  iron  is  sur- 
rounded by  a  coil  or  helix  of  wire  and  a  magnet  is 
approached  to  or  drawn  from  the  bar,  a  current  of  elec- 
tricity is  induced  in  the  coil.  Further,  he  found  that  when 
one  pole  of  the  magnet  was  approached  to  the  bar,  the 
electrical  current  had  a  direction  opposite  to  that  electrical 
current  produced  when  the  magnet  was  receded  from,  the 
bar :  also  that  the  opposite  poles  of  the  magnet  had 
opposite  actions,  or,  in  other  words,  produced  by  the  same 
movement  currents  of  opposite  directions.  His  researches 
proved  that  the  soft  iron  and  the  magnet  might  change 
places,  and  that,  generally,  electric  currents  were  produced 
in  a  coil  placed  in  a  magnetic  field,  either  by  changes  of 
intensity  of  this  magnetic  field,  or  by  the  coil  being  made 
to  cut  through  magnetic  rays  of  different  intensities. 


2  ;   ELECTRIC   TRANSMISSION  OF  POWER, 

The  practical  application  of  this  important  addition  to 
electrical  knowledge  soon  appeared  in  the  first  magneto- 
electric  machine,  constructed  in  1833,  by  Pixii.  In  this 
machine  a  horse-shoe  magnet  was  caused  to  revolve  with 
its  poles  before  those  of  a  double  electro-magnet.  This 
machine  had  the  mechanical  disadvantage  that  the  heavier 
part,  the  permanent  magnet,  was  put  in  motion.  Clarke 
improved  upon  this  construction  in  machines  of  small 
dimensions,  the  magnets  in  which  were  fixed,  and  the  coil 
caused  to  rotate.  Machines  virtually  on  the  principle 
of  Clarke's  machine,  but  of  larger  size,  were  soon  con- 
structed by  Holmes,  of  London,  and  the  Compagnie 
1'Alliance,  of  Paris.  All  these  machines  may  be  classed 
as  magneto-electric,  that  is  to  say,  the  current  produced 
depends  upon  the  action  of  magnets  upon  an  electrical 
circuit. 

Magneto-electric  machines  are  quite  distinct  from 
electro-magnetic  machines,  in  which  the  electrical  current 
is  made  to  produce  movement,  being  itself  generated  by 
a  source  foreign  to  the  motor. 

Magneto-electric  machines  are  disadvantageous  in  use, 
because  their  effect  does  not  increase  with  their  dimensions, 
and  machines  for  the  production  of  powerful  currents 
become  cumbersome  and  costly.  The  rapid  rotation,  and 
consequently  rapid  reversals  of  magnetism  of  the  iron 
core,  give  rise  to  great  heating  of  the  working  parts,  and 
to  the  necessity  of  cooling  these  with  water.  The  step 
from  magneto-electric  to  dynamo-electric  machines  was 
due  to  Mr.  S.  Alfred  Varley,  Sir  Charles  Wheatstone,  and 
Dr.  Werner  Siemens,  who  quite  independently  discovered 
and  worked  upon  the  same  principle  of  accumulation  by 
mutual  action,  the  priority  falling  to  Mr.  Varley  by  his 
patent.  In  this  construction  of  machine,  induced  currents 
are  caused  to  circulate  in  the  electro-magnet  coils  that 
produce  them,  and  are  in  this  way  increased.  By  this 
mutual  action  currents  are  produced,  the  limit  of  intensity 


DYNAMO-ELECTRIC   MACHINES.  6 

of  which  is  co-equal  with  the  maximum  limit  of  magnetic 
saturation. 

This  principle  of  accumulation  by  mutual  action  is  now 
employed  in  all  machines  where  currents  of  great  intensity 
are  required. 

As  all  these  machines  can  be  made  to  yield  electricity, 
through  rotation  imparted  to  them  by  the  expenditure  of 
mechanical  power,  so  can  this  power  be  reclaimed,  in  part, 
by  causing  the  current  generated  by  one  machine  to  be 
passed  into  the  coils  of  a  second  machine.  This  second 
machine  will  then  rotate  in  an  opposite  direction,  about 
50  per  cent,  of  the  mechanical  power  expended  upon 
the  pulley  of  the  first  machine  being  obtainable  from 
the  pulley  of  the  second.  This  is  the  basis  of  electrical 
transmission  of  power. 


B  2 


ELECTRIC  TRANSMISSION   OF   FOWEK. 


CHAPTEE  II. 

THE   GRAMME   MACHINE. 


THE  machine  invented  by  M.  Gramme  is  essentially  the 
parent  of  present  dynamo-electric  machines.  To  compre- 
hend the  principle  of  the  Gramme  machine,  let  Fig.  1 


FIG.  1. 


represent  a  magnetised  bar,  A  B,  and  a  conducting  helix, 
capable  of  moving  to  and  fro  on  the  bar.  If  the  helix  is 
brought  towards  the  bar  from  its  position  at  X,  an 
induced  current  is  produced  at  each  movement.  These 
currents  are  in  the  same  direction  while  the  helix  passes 
the  middle,  M,  of  the  bar,  A  B,  until  it  leaves  the  opposite 
pole,  B.  Thus,  in  the  entire  course  of  the  helix  on  to  and 
from  the  magnet,  two  distinct  periods  are  to  be  distin- 
guished :  in  the  first  half  of  the  movement  the  currents 
are  direct,  and  in  the  second  they  are  inverted.  If,  instead 
of  moving  from  left  to  right,  as  we  have  supposed,  the 
movement  is  from  right  to  left,  everything  occurs  as 
before,  with  the  exception  that  the  currents  are  opposite. 
Let  two  magnets,  A  B,  and  B'  A'  (Fig.  2),  be  placed  end 
to  end,  in  contact  by  poles  of  the  same  name,  B  B'.  The 
whole  forms  a  single  magnet  with  a  consequent  point  at 


THE  GRAMME  MACHINE.  5 

the  centre.  If  the  helix  is  moved  with  relation  to  this 
system,  it  is  traversed  by  a  positive  current  during  the 
first  movement,  between  A  and  B ;  by  a  negative  current 

FIG  2. 


FIG.  3. 


in  the  second,  from  B  to  B' ;  again  by  a  negative  current 
in  the  third,  from  B'  to  A';  and  finally  by  a  positive 
current,  when  leaving  A'. 

Eeplacing  the  straight  magnets  by  two  semi-circular 
magnets  (Fig.  3),  put  end  to  end,  the  poles  of  the  same 
name  together,  there  occur 
the  two  poles,  A  A',  B  B', 
and  the  results  are  the 
same  as  in  the  preceding, 
MM'  being  the  two  neutral 
points. 

The  essential  part  of  the 
Gramme  machine  is  a  soft- 
iron  ring,  furnished  with 
an  insulated  copper  helix 
wound  on  the  whole  length 
of  the  iron.  The  extre- 
mities of  this  helix  are 
soldered  together,  so  as  to 
form  a  continuous  wire  without  issuing  or  re-entrant  end. 
If  the  wire  is  denuded  exteriorly,  the  part  bared  forms 
a  straight  band  running  round  the  whole  of  the  circum- 
ference Friction-pieces,  M  and  M',  are  applied  to  the 
bared  part  of  the  helix.  When  the  ring  is  placed  before 
the  poles,  S  and  N,  of  a  magnet,  the  soft  iron  is  magnetised 


6  ELECTRIC  TRANSMISSION   OF  POWER. 

by  induction,  and  there  occur  in  the  ring  two  poles, 
N'  and  S',  opposed  to  the  poles  S  and  N.  If  the  ring 
revolves  between  the  poles  of  a  permanent  magnet,  the 
induced  poles  developed  in  the  ring  always  remain  in  the 
same  relation  with  regard  to  the  poles  N  and  S,  and  are 
subject  to  displacement  in  the  iron  itself  with  a  velocity 
equal,  and  of  contrary  direction,  to  that  of  the  ring. 
Whatever  may  be  the  rapidity  of  the  movement,  the  poles 
N'  S'  remain  fixed,  and  each  part  of  the  copper  helix 
Successively  will  pass  before  them. 

An  element  of  this  helix  will  be  the  locale  of  a  current 

FIG.  4. 


of  a  certain  direction  when  traversing  the  path  M  S  M' 
(Fig  4),  and  of  a  current  of  inverse  direction  to  the  first 
when  passing  through  the  path  M'  N  M.  And,  as  all  the 
elements  of  the  helix  possess  the  same  property,  all  parts 
of  the  helix  above  the  line  M  M'  will  be  traversed  by  cur- 
rents of  the  same  direction,  and  all  parts  beneath  the  line 
by  a  current  of  inverse  direction  to  the  preceding. 

These  two  currents  are  evidently  equal  and  opposite, 
and  balance  one  another.  When  two  voltaic  batteries, 
composed  of  the  same  number  of  elements,  are  coupled  in 
opposition,  it  is  necessary  only  to  put  the  extremities  of  a 
circuit  in  communication  with  the  poles  common  to  the 


THE  GRAMME   MACHINE.  7 

two  batteries,  and  the  currents  become  associated  in 
quantity. 

M.  Gramme  collects  the  currents  developed  in  the  ring 
of  his  machine  by  establishing  collectors  on  the  line  M  M', 
where  the  currents  in  contrary  direction  encounter  each 
other. 

In  practice,  Gramme  does  not  denude  the  wire  of  the 
ring.  Fig.  5  shows  the  wire  and  coils.  One  or  two  coils 


B 


(B)  are  shown  in  position,  and  with  the  iron  ring  laid 
bare,  and  cut. 

Insulated  radial  pieces,  E,  are  each  attached  to  the 
issuing  end  of  a  coil,  and  to  the  entrant  end  of  the  follow- 
ing coil.  The  currents  are  collected  on  the  pieces,  E,  as 
they  would  be  on  the  denuded  wire.  Their  bent  parts, 
brought  parallel  to  the  axle,  are  carried  through  and 
beyond  the  interior  of  the  ring,  and  are  brought  near 
one  another  upon  a  cylinder  of  small  diameter.  The 
friction-brushes  on  the  pieces  are  in  a  plane  perpendicular 
to  the  polar  line  S  and  N — that  is,  at  the  middle  or 
neutral  points  M  and  M'.  The  intensity  of  the  current 


8 


ELECTEIC  TRANSMISSION  OF  POWER. 


increases  with,  the  velocity  of  rotation  ;  the  electro-motive 
force  is  proportional  to  the  velocity.  Gramme  modifies 
his  machine  so  as  to  produce  effects  of  tension  or  of 


quantity,  by  winding  the  ring  with  fine  or  coarse  wire. 
With  equal  velocities  of  the  ring  the  electric  tension  will 
be'  proportional  to  the  number  of  convolutions  of  the  wire. 


THE   GRAMME   MACHINE. 


9 


Figs.  6  and  7  represent  a  Gramme  machine ;  it  consists 
of  two  flanks  of  cast  iron,  arranged  vertically,  and  con- 
nected by  four  iron  bars,  serving  as  cores  to  electro- 
magnets. The  axle  is  of  steel ;  its  bearings  are  relatively 
very  long.  The  central  ring  has  two  wires  wound  parallel 


FIG.  7. 


on  the  soft  iron,  and  connected  to  two  collectors  to  re- 
ceive the  currents.  The  poles  of  the  electro-magnet  are 
of  large  size,  and  embrace  seven-eighths  of  the  total  cir- 
cumference of  the  central  ring.  Four  brushes  collect  the 
currents  produced.  The  electro-magnet  is  placed  in  the 
circuit.  The  total  length  of  the  machine,  pulley  included, 


10  ELECTRIC  TRANSMISSION  OP  POWER. 

is  31 J  inches,  its  width.  1  foot  9J  inches,  and  its  height 
23  inches.     Its  weight  is  880  Ibs. 

The  double  coil  is  connected  to  120  conductors,  60  on 
each  side.  Its  exterior  diameter  is  27  inches ;  the  weight 
of  wire  wound  on  is  31  Ibs.  The  electro-magnet  bars  have 
a  diameter  of  2J  inches,  and  a  length  of  15 1  inches.  The 
total  weight  of  wire  wound  on  the  four  bars  is  211  Ibs. 
The  winding  of  the  wires  on  the  ring  is  effected  as  if  two 
complete  bobbins  were  put  one  beside  the  other,  and 
these  two  bobbins  may  be  connected  in  tension  or  in 
quantity. 


THE   BKUSH   MACHINE. 


11 


CHAPTER  III. 


THE   BRUSH   MACHINE. 


MR.  BRUSH,  the  inventor  of  the  machine  bearing  his  name, 
considers  that  even  the  best  forms  of  magneto-electric 
apparatus  are  unnecessarily  bulky,  heavy,  and  expensive, 
and  are  more  or  less  wasteful  of  mechanical  power.  The 
armature  of  the  Brush  machine  (Figs.  8  to  11)  is  of 


FJG.  8. 


iron,  in  the  form  of  a  ring,  and  is  attached  to  a  hub, 
which  is  rigidly  attached  to  the  shaft  C  (Fig.  8).  The 
armature,  instead  of  having  a  uniform  cross  section,  as  in 
the  Gramme  machine,  is  provided  with  grooves,  or  depres- 
sions, in  a  direction  at  right  angles  with  its  magnetic 


12  ELECTRIC   TRANSMISSION  OF  POWER. 

axis  or  length.  These  grooves  are  wound  full  of  insulated 
copper  wire,  and  are  of  any  suitable  number.  The  advan- 
tage of  winding  the  wire  on  the  armature  depressions  is 
twofold.  The  projecting  portion  of  the  armature  between 
the  sections  of  wire  may  be  made  to  revolve  very  close  to 
the  poles  N  N  and  S  S  of  the  magnets,  from  which  the 
magnetic  force  is  derived,  thus  utilising  the  inductive 
force  of  the  latter  to  a  much  greater  extent  than  is  possible 
in  the  case  of  annular  armatures  entirely  covered  with 
wire,  which  therefore  cannot  be  brought  very  near  the 
magnets.  Owing  to  the  exposure  of  a  very  considerable 
portion  of  the  armature  to  the  atmosphere,  the  heat,  which 
is  always  developed  by  the  rapidly  succeeding  magnetisa- 
tions and  demagnetisations  of  armatures  in  motion,  is 
rapidly  dissipated  by  radiation  and  convection.  In  the 
case  of  armatures  completely  covered  with  wire,  the 
escape  of  heat  is  very  slow,  so  that  they  must  be  run  at  a 
comparatively  low  rate  of  speed,  with  corresponding  effect, 
in  order  to  prevent  injurious  heating.  Opposite  sections 
on  the  armature  may  have  their  first  or  their  last  ends 
joined  together,  and  their  remaining  ends  connected  with 
two  segments  of  metal  of  the  commutator  cylinder  E, 
which  is  carried  by  the  shaft  C,  and  is  of  insulating 
material  (Fig.  9). 

The  two  metal  segments 
are  placed  opposite  each 
other  on  the  cylinder, 
and  are  each  of  a  length 
less  than  half  the  cir- 
cumference of  the  latter, 
thus  exposing  the  in- 
sulating cylinder  in 
two  places  diametrically 
opposite  each  other  and 
alternating  with  the 
metal  segments.  The  two  segments,  say  S3  and  S7,  cor- 


THE   BRUSH  MACHINE.  13 

responding  to  sections  3  and  7  of  wire,  hold  a  position 
on  the  cylinder  in  advance  of  those  of  the  preceding 
sections  S2  and  S6  to  the  same  angular  extent  that  the 
sections  3  and  7  in  question  are  in  advance  of  sections 
2  and  6.  In  this  arrangement  the  number  of  segments 
is  equal  to  the  number  of  sections,  each  segment  being 
connected  with  but  one  section.  The  first  and  last  ends 
of  each  section  can,  however,  be  attached  to  two  opposite 
segments,  the  commutator  cylinder,  in  that  case,  being 
constructed  with  double  the  number  of  segments  as  in 
the  former  case,  thus  making  the  number  of  segments 
double  the  number  of  sections.  Two  metallic  plates 
or  brushes,  insulated  from  each  other,  press  lightly  upon 
the  cylinder  E  at  opposite  points,  so  selected  that  while 
each  section  of  wire  on  the  armature  is  passing  from 
one  neutral  point  to  the  other,  the  corresponding  seg- 
ments on  the  cylinder  will  be  in  contact  with  them. 
These  plates  or  brushes  collect  the  currents  of  electricity 
generated  by  the  revolution  of  the  armature,  one  being 
positive  and  the  other  negative.  When  the  section 
of  wire  is  .passing  the  neutral  points  on  the  arma- 
ture, the  plates  are  in  contact  with  the  insulating 
material  of  the  cylinder  between  the  corresponding  seg- 
ments, thus  cutting  the  section,  which  is  at  the  time 
useless,  out  of  the  circuit  altogether.  The  necessity  for 
thus  insulating  each  section  from  the  plates  during  the 
time  it  is  inactive  becomes  obvious  when  it  is  considered 
that,  if  this  were  not  done,  the  idle  section  would  afford 
a  passage  for  the  current  generated  in  the  active  sections. 
During  the  time  a  section  or  bobbin  is  passing  from  one 
neutral  point  of  the  armature  to  the  next  one,  an  electric 
impulse,  constant  in  direction,  but  varying  in  electro- 
motive force,  is  induced  in  it.  This  electro-motive  force, 
starting  from  nothing  at  the  neutral  point,  quickly  in- 
creases to  nearly  its  maximum,  and  remains  almost  con- 
stant until  the  section  is  near  the  next  neutral  point, 


14  ELECTRIC   TRANSMISSION  OF  POWER. 

when   it  rapidly  falls  to   zero  as  the  neutral  point   is 
reached. 

The  insulating  spaces  are  made  of  such  a  length  that  a 
section  or  bobbin  is  cut  out  of  the  circuit,  not  only  when 
it  is  at  the  neutral  points,  but  also  during  the  time  when 
its  electro-motive  force  is  rising  and  falling  at  the 
beginning  and  end  of  an  impulse. 

If  the  insulating  space  is  too  short,  so  as  to  keep  or 
bring  a  section  in  the  circuit,  while  its  electro-motive 
force  is  low,  then  the  current  from  the  other  sections, 
being  of  superior  electro-motive  force,  will  overcome  this 
weak  current  and  discharge  through  this  section.  If  the 
insulating  spaces  are  a  little  longer  than  necessary,  no 
material  inconvenience  results.  A  suitable  length  for 
practical  purposes  is  easily  determined  experimentally. 
It  is  found  in  practice  that  the  neutral  points  of  the 
armature  in  motion  are  considerably  in  advance  of  their 
theoretical  position,  this  circumstance  being  attributed  to 
the  time  required  to  saturate  any  point  of  the  armature 
with  magnetism,  so  that  the  given  point  is  carried  beyond 
the  point  of  greatest  magnetic  intensity  of  the  field  before 
receiving  its  maximum  charge.  M.  Gramme  however  be- 
lieves it  due  to  the  reaction,  by  induction,  of  the  armature 
coils  upon  the  cores  and  coils  of  the  electro-magnet. 

It  is  necessary  to  adjust  the  commutator  cylinder  on 
the  revolving  shaft  of  the  machine  with  special  reference 
to  the  neutral  points  of  the  armature  when  in  motion, 
in  order  that  its  insulating  space  may  correspond  with 
the  neutral  points.  This  adjustment  is  made  experi- 
mentally as  follows :  The  commutator  cylinder  having  been 
placed  approximately  in  its  proper  position,  the  machine 
is  started,  and  the  presence  or  absence  of  sparks  at  the 
points  of  contact  between  the  plates  and  commutator 
cylinder  is  noted.  If  sparks  occur,  the  commutator 
cylinder  is  turned  slightly  forward  or  backward  on  its 
axis,  until  the  sparks  disappear. 


THE   BRUSH   MACHINE.  15 

The  presence  of  sparks  when  the  commutator  is  even 
slightly  out  of  its  proper  position  is  easily  explained. 
If  a  break  between  a  pair  of  segments  and  the  plates  oc- 
curs while  the  corresponding  section  of  wire  on  the  arma- 
ture is  still  active,  a  spark  is  produced  by  the  interruption 
of  the  current,  while  if  the  break  occurs  too  late  the 
section  in  question  will  have  become  neutral,  and  then 
commenced  to  conduct  the  current  from  the  active  sec- 
tions, and  the  interruption  of  this  passage  causes  a  spark  in 
this  instance.  If  the  commutator  is  much  removed  from 
its  proper  position  in  either  direction,  the  sparks  are  so 
great  as  to  very  rapidly  destroy  both  the  commutator 
and  the  brushes,  while  the  current  from  the  machine  is 
correspondingly  diminished. 

With  the  arrangement,  where  the  first  and  last  ends  of 
each  of  two  opposite  sections  are  attached  to  two  opposite 
segments  the  intensity  of  the  induced  electrical  current 
will  be  that  due  to  the  length  of  wire  in  a  single  section 
only,  while  the  quantity  will  be  directly  as  the  number 
of  sections.  By  doubling  the  size  of  each  bobbin,  and 
diminishing  their  number  one  half,  a  current  of  double 
the  intensity  and  one  half  the  quantity  of  the  former  will 
be  obtained.  This  effect,  however,  can  be  secured  in 
another  manner,  by  connecting  the  first  and  last  ends  of 
the  two  opposite  sections  together,  and  joining  the  re- 
maining ends  only  to  two  opposite  segments,  as  illustrated 
in  Fig.  10.  This  arrange- 
ment is  found  most  con-  FlG*  "' 
venient  in  practice. 

The  arrangement  of  the 

cylinder  E  with  segments     /  i    /       T — V-\-  \{ZTff  ~~7^\ 
S  (Fig.  9)  is  usually  re-     ((   (       /  j/-~fel^     (    ) 
placed     by     another,     in 
which  the  last  end  of  one 
section  and  the  first  end 
of  the  succeeding  may  be  connected  with  a  strip  of  metal 


16  ELECTRIC   TRANSMISSION  OF   POWER. 

attached  to  the  cylinder,  parallel  with  its  axis,  as  in  the 
Siemens  and  Gramme  machines.  These  metallic  strips  or 
conductors  are  equal  in  number  to  the  sections  of  wire  on  the 
armature,  and  are  insulated  from  each  other.  The  plates 
press  upon  the  cylinder,  in  this  case,  at  points  correspond- 
ing to  the  neutral  points  of  the  armature,  thus  being  at 
right  angles  with  their  position  in  the  first  arrangement. 
This  plan,  which  is  the  one  commonly  used  with  annular 
armatures,  gives  fair  results,  but  is  subject  to  a  serious 
disadvantage  from  which  the  first  is  free.  The  difficulty 
is,  that  the  sections  of  wire,  when  at  or  near  the  neutral 
points  of  the  armature,  contribute  little  or  no  useful  effect, 
but  the  current  from  the  other  sections  must  pass  through 
these  in  order  to  reach  the  plates,  thus  experiencing  a 
considerable  and  entirely  useless  resistance ;  and,  owing  to 
the  opposite  directions  of  the  currents  through  the  active 
sections  on  opposite  sides  of  the  neutral  points,  these  cur- 
rents, by  passing  through  the  idle  sections,  tend  strongly 
to  produce  "consequent"  points  in  the  armature  where  the 
neutral  points  should  be,  thus  interfering  seriously  with 
the  theoretical  distribution  of  the  magnetism  of  the 
armature.  The  electro-magnets  H  are  excited  by  the 
whole  or  a  portion  of  the  electric  current  derived  from 
the  revolving  armature,  as  is  usual  in  apparatus  of  this 
kind,  the  novel  feature  of  this  part  of  the  machine  con- 
sisting of  the  manner  in  which  the  magnetic  poles  are 
presented  to  the  armature  ;  this  arrangement  is  such  that 
a  very  large  proportion  of  the  entire  surface  of  the  arma- 
ture is  constantly  presented  to  the  poles  of  the  magnets, 
thus  securing  uniformity  of  magnetisation,  as  well  as 
maximum  amount.  The  iron  segments,  constituting  the 
poles  of  the  magnets,  are  arranged  on  both  sides  of  the 
armature.  The  pieces  N  N,  or  S  S,  may  be  connected  at 
their  outer  edges,  thus  forming  one  piece,  and  enclosing 
the  armature  still  more.  In  the  other  dynamo-electric 
machines  no  magnetic  field  is  maintained  when  the  ex- 


THE   BKUSH  MACHINE. 


17 


ternal  circuit  is  opened,  except  that  due  to  residual  mag- 
netism; hence  the  electro-motive  force  developed  by 
the  machine  in  this  condition  is  very  feeble.  It  is  only 
when  the  external  circuit  is  closed  through  a  resistance 


\\ 


not  too  large  that  powerful  currents  are  developed,  owing 
to  the  strong  magnetic  field  produced  by  the  circulation 
of  the  currents  themselves  around  the  field  magnets. 
By  diverting  from  external  work   a  portion   of   the 

c 


18  ELECTEIC   TRANSMISSION   OF   POWER. 

current  of  the  machine,  and  using  it  either  alone,  or  in 
connection  with  the  rest  of  the  current  for  working  the 
field  magnets,  a  permanent  field  may  be  obtained. 

Mr.  Brush  winds  the  cores  of  the  field  magnets  with  a 
quantity  of  a  comparatively  fine  wire,  having  a  high 
resistance  in  comparison  with  that  of  the  external  circuit, 
and  the  rest  of  the  wire  in  the  machine.  The  ends  of 
this  wire  are  so  connected  with  other  parts  of  the  machine 
that  when  the  latter  is  running,  a  current  of  electricity 
constantly  circulates  in  the  wire,  whether  the  external 
circuit  be  closed  or  not.  The  high  resistance  of  -this  wire 
prevents  the  passage  through  it  of  more  than  a  small 
proportion  of  the  whole  current  capable  of  being  evolved 
by  the  machine  ;  therefore  the  available  external  current 
is  not  materially  lessened.  When  this  device,  called  a 
"  teaser,"  is  used  in  connection  with  field  magnets,  also 
wound  with  coarse  wire  (Fig.  11),  for  the  purpose  of  still 
further  increasing  the  magnetic  field  by  employing  the 
main  current  for  this  purpose,  then  the  "teaser"  may  be 
so  arranged  that  the  current  which  passes  through  it  will 
also  circulate  in  the  coarse  wire,  thus  increasing  efficiency 


THE    WALLACE-FARMER   AND   SIEMENS   MACHINES.     19 


CHAPTER   IV. 

THE   WALLACE-FARMER   AND   SIEMENS   MACHINES. 

IN  the  Wallace-Farmer  machine  (Fig.  12)  the  magnetic 
field  is  produced  by  two  horse-shoe  electro-magnets,  but 
with  poles  of  opposite  character  facing  each  other. 

FIG.  12. 


Between  the  arms  of  the  magnets,  and  passing  through 
the  uprights  supporting  them,  is  the  shaft,  carrying  at  its 
centre  the  rotating  armature.  This  consists  of  a  disc  of 
cast  iron,  near  the  periphery  of  which,  and  at  right  angles 
to  either  face,  are  iron  cores,  wound  with  insulated  wire, 
thus  constituting  a  double  series  of  coils.  The  armature 

c2 


20 


ELECTRIC   TRANSMISSION  OF  POWER. 


coils  (Figs.  13  and  14)  being  connected  end  to  end,  the 
loops  so  formed  are  connected  in  the  same  manner,  and 
to  a  commutator  of  the  same  construction  as  that  of  the 
Gramme.  As  the  armature  rotates,  the  cores  pass  between 
the  opposed  north  and  south  poles  of  the  field  magnets, 
and  the  current  generated  depends  on  the  change  of 


FIG.  13. 


FIG.  14. 


polarity  of  the  cores.  It  will  be  seen  that  this  constitutes 
a  double  machine,  each  series  of  coils,  with  its  commutator, 
being  capable  of  use  independently  of  the  other ;  but  in 
practice  the  electrical  connections  are  so  made  that  the 
currents  generated  in  the  two  series  of  armature  coils  pass 
through  the  field  magnet  coils,  and  are  joined  in  one 
external  circuit. 

This  form  of  armature  also  presents  considerable  un- 
covered surface  of  iron  to  the  cooling  effect  of  the  air,  but, 
like  that  of  the  Brush,  presents  considerable  resistance  to 
rotation. 

In  the  Wallace-Farmer  machine  there  is  considerable 
heating  of  the  armature,  the  temperature  being  sometimes 
sufficiently  high  to  melt  sealing-wax. 

In  the  Siemens  machine,  the  conductor  of  insulated 
copper  wire  is  coiled  in  several  lengths  and  convolutions 


THE   WALLACE-FARMER  AND   SIEMENS  MACHINES.     21 

upon  a  cylinder  shown  in  transverse  (Fig.  15),  and  in  end 
view  by  Fig.  16.      Each  convolution  is  parallel  to  the 

FIG.  15. 


longitudinal  axis  of  the  cylinder,  and  the  whole  surface  of 
the  cylinder  is  covered  with  wire,  laid  on  in  six  sections. 


FIG.  16. 


Surrounding  the  wire  cylinder  for  about  two-thirds  of  its 
surface  are  curved  iron  bars,  the   space  between   these 


22  ELECTRIC   TRANSMISSION   OF  POWER. 

curved  bars  and  the  wire  cylinder  being  as  small  as  is 
consistent  with  the  free  rotation  of  the  cylinder.  The 
curved  bars  are  themselves  the  prolongations  of  the  cores 
of  large  flat  electro-magnets;  the  coils  of  these  electro- 
magnets and  the  wire  of  the  cylinder  (from  brush  to 
brush)  forms  a  continuous  electrical  circuit.  Upon  revo- 
lution of  the  wire  cylinder,  which  is  supported  upon  a 
longitudinal  axis  in  proper  bearings,  the  axis  carrying  a 
pulley,  a  current  is  generated  in  it,  and  this  current, 
initially  weak,  is  directed  into  the  coils  of  the  electro- 
magnets, magnetising  the  cores,  which  induce  a  still 
stronger  current  in  the  wire  cylinder.  This  mutual 
action  continues  until  the  magnetic  limit  of  the  iron  is 
attained.  At  every  revolution  of  the  wire  cylinder,  the 
maximum  magnetic  power  acting  upon  each  convolution 
is  attained  when  the  convolution  passes  through  the 
middle  of  both  magnetic  fields,  and  this  power  falls  to 
zero  when  the  convolution  is  perpendicular  to  that 
position.  Each  convolution  is  therefore  subject  to  a 
neutral  position,  and  by  Lenz's  law  a  convolution  starting 
from  that  position  on  the  one  side  of  the  axis  towards  the 
north  pole  of  the  electro-magnet  would  be  subject  to  a 
direct  induced  current,  and  that  portion  of  the  convolution 
on  the  opposite  side  of  the  axis  will  be  traversed  by  a 
current  of  opposite  direction,  as  regards  a  given  point, 
but  of  the  same  direction  as  regards  circuit. 

Each  of  the  six  sections  of  wire  coiled  upon  the  cylinder 
consists  of  two  separate  coils,  the  whole  having  twenty- 
four  ends ;  two  of  these  ends  are  brought  to  each  of  the 
segments  of  a  circular  commutator  in  such  a  manner 
that  the  whole  six  double  sections  form  a  continuous 
circuit,  but  not  one  continuous  helix. 

In  order  that  the  segments  may  be  properly  presented 
to  the  collecting  brushes,  the  connections  are  arranged 
according  to  their  relative  momentary  position.  The 
electric  currents  are  collected  upon  two  wire  brushes 


THE   WALL  ACE- FARMER   AND   SIEMENS   MACHINES.     23 


tangential  to  the  segments  of  the  commutator,  and  these 
brushes  form,  through  the  electro-magnets,  the  two  elec- 
trodes of  the  machine ;  and  to  the  electro-magnet  ends  are 
connected  the  conducting  wires  leading  to  the  system 
where  the  current  is  to  be  utilised. 

The  dimensions,  weights,  number  of  revolutions  made 
by  the  cylinder,  and  HP.  required  for  driving,  are  for 
three  sizes  of  the  machine,  as  under  : — 


Dimension  in  laches. 

Weight 
in  Ibs. 

Revolutions 
of 
Cylinder. 

HP. 

Length. 

Width. 

Height. 

25 

21-0 

8-8 

298 

1,100 

U  to    2 

29 

26-0 

9-5 

419 

850 

3     „     3^ 

44 

28-3 

12-6 

1,279 

480 

9     „  10 

24  ELECTKIC  TRANSMISSION  OF  POWER. 


CHAPTER  V. 

EFFICIENCY   OF   DYNAMO-ELECTRIC   MACHINES. 

WHEN  two  machines  are  coupled  in  circuit  for  the  trans- 
mission of  the  power  of  a  prime  mover,  we  may  consider 
two  causes  of  efficiency :  (1)  that  of  the  first  machine  as  a 
current  generator,  and  (2)  that  of  the  two  machines  con- 
sidered together  as  a  transmitting  system.  In  a  paper 
read  before  the  Institution  of  Mechanical  Engineers,  by 
Dr.  Hopkinson,  it  has  been  pointed  out  that  it  is  desirable 
to  know  what  dynamo-electric  machines  can  do  with 
varied  and  known  resistances  in  the  circuit  and  with 
varied  speeds  of  rotation ;  and  what  amount  of  power  is 
absorbed  in  each  case. 

The  mechanical  energy  communicated  by  the  steam- 
engine  or  other  motor  is  not  immediately  converted  into 
the  energy  of  heat,  but  is  first  converted  into  the  energy 
of  an  electric  current  in  a  conducting  circuit.  The  whole 
of  what  is  needed  to  be  known  may  be  more  easily  ascer- 
tained and  expressed  if  the  subject  of  inquiry  is  stated  as  : 
what  current  a  machine  will  produce  under  various  con- 
ditions of  circuit ;  and  at  what  expenditure  of  mechanical 
power.  The  subject  has  been  treated  more  or  less  by 
Edlund  (Pogg.  Annal.,  1867  and  1868),  Houston  and 
Thomson  in  America,  Mascart  ('Journal  de  Physique,' 
March  1878),  Trowbridge  ('Philosophical  Magazine,' 
March  1879),  Schwendler  (' Eeport  on  Electric  Light 
Experiments ').  Dr.  Hopkinson  limits  his  inquiry  to  an 
account  of  some  experiments  on  the  production  of  currents 
by  a  Siemens  medium-sized  machine,  the  machine  which 


EFFICIENCY  OF  DYNAMO-ELECTKIC   MACHINES.      25 

is  said  to  produce  a  light  of  6000  candles,  by  an  expendi- 
ture of  3£  HP.  The  intensity  of  the  magnetic  field  in 
such  machines  as  the  Siemens  and  ordinary  Gramme 
machines  may  be  regarded  as  a  function  of  the  current 
passing ;  to  learn  what  this  function  is  for  the  machine  in 
question,  we  may  construct  a  curve  in  which  the  abscissae 
represent  currents  passing,  and  the  ordinates  the  electro- 
motive force  for  a  given  speed  of  rotation.  But  the  power 
of  a  current,  that  is  its  energy  per  second,  is  the  product 
of  the  electro-motive  force  and  its  intensity ;  this  is  in  all 
cases  less  than  the  power  required  to  drive  the  machine, 
and  the  ratio  between  the  two  may  fairly  be  called  the 
efliciency  of  the  machine.  Consider  the  case  of  a  pump 
forcing  water  through  a  pipe  against  friction ;  then 
electric  current  corresponds  to  the  water  passing  per 
second,  and  electro-motive  force  to  the  difference  of 
pressure  on  the  two  sides  of  the  pump ;  and  just  as  the 
product  of  pressure  and  volume  per  second  is  power,  so 
the  product  of  electro-motive  force  and  current  is  power ; 
which  is  directly  comparable  with  the  power  expended  in 
driving  the  machine  or  the  pump,  as  the  case  may  be. 
The  peculiarity  of  the  so-called  dynamo-electric  machine 
lies  in  this,  that  which  corresponds  to  the  difference  of 
pressure  (the  electro-motive  force)  depends  directly  on 
what  corresponds  to  the  volume  passed  (the  current). 
Each  experiment  requires  the  determination  of  the  speed, 
the  driving  power,  the  resistances  in  oironit,  and  the 
current  passing. 

In  Dr.  Hopkinson's  measurements,  the  speed  of  the 
steam  engine  was  maintained  very  constant  by  means  of  a 
governor  specially  arranged  for  great  sensitiveness.  The 
speed  was  varied  by  means  of  a  weight  and  a  spring, 
attached  to  a  lever  on  the  throttle-valve  spindle.  The 
power  was  transmitted  from  the  engine  to  a  countershaft 
by  means  of  a  strap,  and  by  a  second  strap  from  the 
countershaft  to  the  pulley  of  the  machine.  On  this  second 


26 


ELECTEIC   TRANSMISSION   OF   POWER. 


strap  was  the  dynamometer  (Fig.  17),  arranged  as  used  by 
the  Author,  and  described  in  a  paper  read  before  the 
Institution  of  Civil  Engineers,  1877-8. 


The  tension  difference  in  the  two  parts  of  the  strap 
of  the  dynamometer  and  the  velocity  of  rotation  of 
the  machine  being  known,  the  power  received  was 


EFFICIENCY   OF   DYNAMO-ELECTRIC   MACHINES.      27 

obtained,  expressed  in  gram-centimetres  per  second. 
Multiplying  by  981,  the  value  of  gravity  in  centimetres 
and  seconds,  the  power  is  then  expressed  in  ergs  *  per 
second,  and  is  ready  for  comparison  with  the  results  of 
the  electrical  experiments. 

The  dynamo-electric  machine  in  these  trials  was  a 
Siemens  medium  size;  the  armature  coil  has  fifty-six 
divisions,  and  the  brushes  are  single,  not  divided — that 
is,  each  brush  is  in  connection  with  one  segment  of  the 
commutator  at  each  instant.  The  leading  wire  was  100 
yards  of  seven  copper  wires,  insulated  with  tape  and  india- 
rubber,  and  having  a  diameter  of  about  9'6  millimetres. 
The  current  passing  was  ascertained  by  the  heating  of  the 
calorimeter,  or  by  measuring  the  difference  of  potential  at 
the  extremities  of  a  resistance,  all  the  resistances  of  the 
circuit  being  known.  The  resistance  coils  comprised  ten 
coils  of  common  brass  wire,  each  wound  round  a  couple  of 
wooden  uprights  driven  into  a  baseboard  common  to  the 
set;  each  wire  was  about  60  metres  long,  and  of  No.  17 
Birmingham  wire-gauge,  weighing  about  14*6  grammes 
per  metre.  Each  terminal  was  connected  to  a  cup  of 
mercury  excavated  in  the  baseboard,  so  that  the  coils 
could  be  placed  in  series  or  in  parallel  circuit  at  pleasure. 
The  resistance  of  each  coil  being  about  3  ohms,  this  set 
could  be  arranged  to  give  resistances  varying  from  0  •  3  to 
30  ohms. 

The  calorimeter  was  a  double  copper  vessel ;  a  resistance 
coil  of  uncovered  German-silver  wire  nearly  2  metres  long, 
1-5  millimetres  in  diameter,  and  having  a  resistance  of  about 
i  ohm,  was  suspended  within  it  from  an  ebonite  cover, 


*  The  dyne  is  the  force  which  will  in  one  second  impart  to  one 
gramme  a  velocity  of  one  centimetre  per  second,  and  an  erg  is  the  work 
done  by  a  dyne  working  through  a  centimetre ;  a  horse-power  may  be 
taken  as  three-quarters  of  an  ergten  per  second,  an  ergten  being 
1010  ergs.  See  Keport  of  Brit.  Assoc.  1873,  and  Everett,  'On  the 
Centimetre-Gramme  Second  System  of  Units.' 


28  ELECTKIC   TRANSMISSION   OF   POWER. 

which  also  carried  a  little  brass  stirrer ;  and  the  calorimeter 
was  filled  with  water  to  the  level  determined  by  the  mark 
of  a  scriber.  It  was,  of  course,  necessary  to  know  the 
capacity  of  the  calorimeter  for  heat.  It  was  filled  with 
warm  water  up  to  the  mark,  and  the  coil  placed  in  posi- 
tion; 120  grammes  of  water  were  then  withdrawn,  and 
the  temperature  of  the  calorimeter  was  observed  to  be 
58  •  8°  centigrade ;  after  the  lapse  of  one  minute  it  was 
58  •  3°  centigrade ;  after  a  second  minute,  57  •  9°  centigrade. 
120  grammes  of  cold  water,  temperature  13*  3°  centigrade, 
were  then  suddenly  introduced  through  a  hole  in  the 
ebonite  cover,  and  it  was  found  that  two  minutes  after 
the  reading  of  57*9°  centigrade,  the  temperature  was 
50  •  0°  centigrade ;  hence  it  was  inferred  that  the  capacity 
of  the  calorimeter  is  equal  to  that  of  750  grammes  of 
water.  The  resistance  coils  were  on  the  binary  scale, 
from  -J-  ohm  to  1024  ohms.  The  battery  was  a  single 
element  of  Daniell's  battery,  in  which  the  sulphate  of 
zinc  solution  floats  on  the  sulphate  of  copper ;  its  electro- 
motive force  is  assumed  to  be  f  volt.  The  resistances 
added  in  the  battery  circuit  are  pencil  lines  on  glass, 
such  as  are  described  in  the  '  Philosophical  Magazine,' 
February,  1879.  Preliminary  to  experiments  on  the  cur- 
rent, determinations  of  resistances  were  made.  When 
the  ends  of  the  cable  were  connected,  the  resistance  was 
found  to  be  0*129  ohm.  The  resistances  in  the  machine 
were  found  to  be  as  follows,  when  cold :  magnet  coils, 
0-156  and  0-152  respectively;  armature  coil,  0-324; 
total,  0*632.  Direct  examination  was  made  of  the  whole 
machine  in  eight  positions  of  the  commutator,  giving 
0  •  643  ohm,  with  a  maximum  variation  from  the  mean  of 
0  •  6  per  cent.  After  running  the  machine  for  some  time, 
the  resistance  was  found  to  be  0  •  683,  an  increase  which 
would  be  accounted  for  by  a  rise  of  temperature  of  12° 
centigrade,  or  thereabouts.  The  resistance  of  the  calori- 
meter is  0  •  20,  without  its  leading  wire,  which  may  bo 


EFFICIENCY   OF   DYNAMO-ELECTRIC  MACHINES.      29 

taken  as  0  •  01.  There  were  thus  three  leading  resistances 
which  must  "be  considered:  (1),  the  resistance  of  the 
machine  and  leading  wire,  assumed  throughout  as  0'8l, 
denoted  by  c^  (2),  the  resistance  of  the  brass  coils,  C, 
calculated  from  the  several  determinations,  with  the  addi- 
tion of  the  resistance  of  the  leading  wire,  0*02,  and 
denoted  by  c2 ;  (3),  when  present,  the  resistance  of  the 
calorimeter  and  leading  wire  denoted  by  c3. 

Two  approximate  corrections  were  employed,  and 
should  be  detailed.  The  first  is  the  correction  for  the 
considerable  heating  of  the  resistance  coils  c.  These 
were  arranged  in  two  sets  of  five  each,  five  being  in 
parallel  circuit,  and  two  sets  in  series.  The  current  from 
the  machine,  being  about  7  *  4  webers  in  each  wire,  was 
passed  for  three  or  four  minutes ;  the  circuit  was  then 
broken,  and  the  resistance  c2  was  determined  within  one 
second  of  breaking  circuit,  when  it  was  found  to  be  about 
5  per  cent,  greater  than  when  cold.  As  the  resistance 
was  falling,  the  following  was  adopted  as  a  rule  of  cor- 
rection :  square  the  current  in  a  single  wire,  and  increase 
the  resistance  c2  by  T^  per  cent,  for  every  unit  in  the 
square.  The  second  correction  is  due  to  the  fact  that 
the  calorimeter  was  losing  heat  all  the  time  it  was 
being  used.  It  was  assumed  that  it  loses  0*01°  centigrade 
per  minute  for  every  1°  centigrade,  by  which  the  tem- 
perature of  the  calorimeter  exceeds  that  of  the  air ;  this 
correction  is,  of  course,  based  on  the  experiment  already 
mentioned. 

The  method  of  calculation  may  now  be  explained : 
E   is   the    total   resistance    of  the    circuit,    equal   to 

ci  4-  C2  +  C3 ; 

Q  is  the  current  passing  in  webers ; 
E  the  electro-motive  force  round  the  circuit  in  volts ; 
Wx  the  work  per  second  converted   into  heat  in   the 

circuit,    as     determined    by    the    galvanometer, 

measured  in  ergtens  per  second ; 


30  ELECTRIC   TRANSMISSION   OF   POWER. 

W2  is  the  work  per  second  as  determined  by  the  calori- 

meter ; 
W3  is  the  work  per  second  as  determined  by  the  dyna- 

mometer, less  the  power   required  to  drive   the 

machine  when  the  circuit  is  open. 
II  P  is  the  equivalent  of  W3  in  HP.  ;  n  is  the  number 

of  revolutions  per  minute  of  the  armature.    Then  : 

Q  =  981  X  X  i, 


T> 

also  W2  =  —  -  multiplied  by  the  mechanical  equivalent  of 

the  heat  generated  per  second  in  the  calorimeter. 

The  accompanying  tables  give  the  results  of  the  ex- 
periments. A  power  of  0-21  ergtens,  or  0*28  HP.,  was 
required  to  drive  the  machine  at  720  revolutions  on  open 
circuit.  An  examination  of  the  table  shows  that  the 
efficiency  of  the  machine  is  about  90  per  cent,  exclusive 
of  friction.  Comparing  experiments  11  and  13,  and  also 
the  last  four  experiments,  it  is  seen  that  the  electro-motive 
force  is  proportional  to  the  speed  of  rotation  within  the 
errors  of  observation.  Experiments  14,  15,  and  16  were 
intended  to  ascertain  the  effect  of  displacing  the  commu- 
tator brushes. 

The  principal  object  of  the  experiments  was  to  ascertain 
how  the  electro-motive  force  depended  on  the  current. 
This  relation  is  represented  by  a  curve  (Fig.  18)  in  which 
the  abscissae  represent  the  currents  flowing,  or  the  values  of 
Q  in  the  table,  and  the  ordinates  the  electro-motive  forces, 
or  the  values  of  E  reduced  to  a  speed  of  720  revolutions 
per  minute.  The  curve  may  also  be  taken  to  represent 
the  intensity  of  the  magnetic  field.  There  will  be  a  point 
of  inflection  in  the  curve  near  the  origin.  The  experi- 
ments 1  to  5  indicate  that  this  is  the  true  form  of  the 
curve,  and  it  is  confirmed  in  a  remarkable  manner  by  a 


EFFICIENCY   OF   DYNAMO-ELECTRIC   MACHINES.      31 

special  experiment.  A  resistance  intermediate  between 
5J  and  4  was  used  in  circuit,  and  E  and  Q  were  deter- 
mined in  two  different  ways  ;  first,  by  starting  with  an 
open  circuit,  which  was  then  closed  ;  secondly,  by  starting 
with  a  portion  of  the  resistance  short  circuited,  and  a  very 
powerful  current  passing,  and  then  breaking  the  short 
circuit.  It  was  found  that  E  and  Q  were  four  times  as 
great  in  the  latter  case  as  in  the  former.  The  curve 
(Fig.  18)  will  also  determine  what  current  will  flow  at 
any  given  speed  of  rotation  of  the  machine,  and  under 
any  conditions  of  the  circuit,  whether  of  resistance  or  of 
opposed  electro-motive  forces.  It  will  also  give  very 
approximate  indications  of  the  corresponding  curve  for 
other  machines  of  the  same  configuration,  but  in  which 
the  number  of  times  the  wire  passes  round  the  electro- 
magnet or  the  armature  is  different. 

It  will  be  well  to  compare  these  results  with  those 
obtained  by  others.  M.  Mascart  worked  on  a  Gramme 
machine  with  comparatively  low  currents ;  he  represents 
his  results  approximately  by  the  formula, 

E  =  »  (a  +  6  Q), 

where  a  and  b  are  constants.  This  corresponds  to  the 
rapidly-rising  part  of  the  above  curve.  Mr.  Trowbridge 
with  a  Siemens  machine  obtained  a  maximum  efficiency 
of  76  per  cent.,  and  states  that  the  machine  was  running 
below  its  normal  velocity.  Mr.  Schwendler's  precis  states 
that  the  loss  of  power  with  a  Siemens  machine  in  pro- 
ducing currents  of  over  20  webers  is  12  per  cent.  Now, 
taking  Dr.  Hopkinson's  experiments,  4  to  19,  the  mean 
value  of  Wx  is  3 '027,  and  of  W3  3-304;  adding  to  the 
latter  0-21,  the  power  required  to  drive  the  machine 
when  no  current  passes,  it  appears  that  13*8  per  cent,  of 
the  power  applied  is  wasted.  Again,  taking  experiments 
4,  6,  8,  10,  and  12,  the  mean  value  of  W2  is  2-888  and  of 
W3,  3*076,  indicating  a  waste  of  power  amounting  to 


32 


ELECTRIC   TRANSMISSION   OF   POWER. 


12  per  cent.    Of  the  loss,  0  •  28  HP.  is  accounted  for  by  fric- 
tion of  the  journals  and  commutator  brush ;  the  remainder 


Electromotor*  *6rc« 


is  expended  in  local  currents,  or  by  loss  of  kinetic  energy 
of  current  when  sparks  occur  at  the  commutator. 


EFFICIENCY   OF   DYNAMO-ELECTRIC   MACHINES.      33 


HCDOO-)H<X>(M'*ih-C<lrtHHO(MT-l 
I-H  i-H  CM  CN  CO  CO  CO  rjn  SO  ^H  CO  ^  -^1 


34  ELECTRIC   TRANSMISSION   OF   POWER. 


CHAPTER  VI. 

PRACTICABILITY    OF  TRANSMISSION   OF   POWER    BY    ELECTRICITY. 

To  deal  with  objections  first,  we  may  regard  the  trans- 
mission of  large  electric  currents  as  considered  by  Mr.  J.  T. 
Sprague,  who  examines  the  suggestions  of  Mr.  Siemens. 
In  a  lecture  delivered  at  Glasgow,  March  14,  1878,  and 
since  published,  Mr.  Siemens  says,  "  The  principal  objec- 
tion that  has  been  raised  by  electricians  to  the  conveyance 
of  power  to  the  distance  of  miles,  is  on  account  of  the  ap- 
parently rapid  increase  in  the  size  of  the  conductor  required 
with  increase  of  distance.  In  order  that  the  magneto- 
electric  machine  may  work  under  the  most  favourable 
conditions,  it  should  have  an  internal  resistance  depending 
in  a  great  measure  upon  the  nature  of  the  work  to  be 
performed,  but  not  exceeding  for  quantative  effects  1  ohm 
or  unit  of  resistance.  If  the  resistance  is  greater,  a  notable 
proportion  of  the  power  expended  will  be  converted  into 
heat  in  the  conductors,  causing  both  loss  of  effect  and 
great  inconvenience.  By  another  law  the  electrical  re- 
sistance of  the  circuit  exterior  to  the  machine  should  be 
somewhat,  but  not  much,  larger  than  the  internal  resistance, 
say  1  •  5  unit.  The  external  resistance  is  composed  of  two 
elements,  namely,  the  conductor,  and  the  resistance  of  the 
electric  lamp  or  electro-magnetic  engine,  which  latter  may 
be  taken  also  as  amounting  to  1  unit,  leaving  only  half  a 
unit  available  for  the  conductor.  These  conditions  deter- 
mine really  the  size  of  the  conductor  for  any  distance  to 
which  the  current  has  to  be  conveyed. 

"  Suppose  the  distance  to  be  half  a  mile,  a  copper  wire 
of  *  23-inch  diameter  will  produce  the  half-unit  resistance, 


PRACTICABILITY   OF   ELECTEIC   TRANSMISSION.      35 

which  is  already  a  wire  of  considerable  dimensions,  for 
the  purpose  of  working  a  single  lamp.  If  the  distance  "be 
doubled  wire  of  the  same  thickness  will  give  twice  the 
electrical  resistance,  and  in  order  to  reduce  it  again  to 
half  a  unit  its  sectional  area  must  be  doubled,  so  that  a 
conductor  of  30  miles'  length  would  require  to  be  602  = 
3,600  times  the  weight  of  the  half-mile  conductor,  and 
this  enormous  increase  in  weight  would  certainly  be  re- 
quired if  the  object  to  be  accomplished  was  the  working 
of  one  electric  lamp  by  a  dynamo-electric  machine.  My 
critics  have,  however,  fallen  into  the  error  of  overlooking 
the  fact  that  half-a-unit  resistance  is  the  same  for  a  circuit 
capable  of  working  one  lamp  as  it  is  for  working  100  or 
1000  lamps. 

"  Electricity  is  not  conducted  upon  the  conditions  ap- 
pertaining to  a  pipe  conveying  a  ponderable  fluid,  the 
resistance  of  which  increases  with  the  square  of  the  velo- 
city of  flow ;  it  is,  on  the  contrary,  a  matter  of  indifference 
what  amount  of  energy  is  transmitted  through  an  electric 
conductor ;  the  only  limit  is  imposed  by  the  fact  that 
in  transmitting  electric  energy,  the  conductor  itself  re- 
tains a  certain  amount  proportional  to  that  transmitted, 
which  makes  its  appearance  therein  in  the  form  of 
heat." 

This  heat,  as  Mr.  Siemens  goes  on  to  explain,  would 
increase  the  resistance  of  the  conductor ;  but  to  simplify 
the  problem  that  heat  and  its  effects  are  not  taken  into 
account  in  the  following  remarks,  Mr.  Sprague  assumes 
that  the  heat  is  radiated  away  or  got  rid  of,  so  as  to  keep 
the  conductor  at  a  uniform  temperature.  According 
to  Mr.  Sprague,  there  are  two  ways  of  regarding  "  re- 
sistance " : — 

1.  In  Ohm's  formulas  it  is  constant  for  all  currents. 
So  is  the  diameter  of  a  pipe  transmitting  water.  The  same 
pipe  will  deliver  any  variable  quantity  or  current  of 
water  corresponding  to  the  pressure;  so  the  same  wire 

D  2 


36  ELECTRIC   TRANSMISSION   OF   POWER. 

will  deliver  any  variable  quantity  or  current  of  electricity 
corresponding  to  the  electro-motive  force.  This  aspect  of 
resistance  then  is  a  mathematical  one,  existing  only  in 
calculations. 

2.  True,  or  practical  resistance,  is  measurable  by  the 
energy  required  to  overcome  it.  The  energy  expended 
by  a  current  in  passing  a  given  conductor  (resistance 
in  the  mathematical  sense  being  simply  the  reciprocal  of 
the  conducting  power  under  unit  condition)  varies  as  the 
square  of  the  current  or  velocity  of  flow. 

Therefore,  electricity  is  really  conducted  under  pre- 
cisely the  "  conditions  appertaining  to  a  pipe  conveying  a 
ponderable  fluid." 

The  resistances  in  a  circuit  are  of  several  orders  : — 

1.  That  of  the  actual  conductor  itself,  which  is  constant. 

2.  Any  work  effected  by  the  current.    This  may  in  some 
cases  be  expressed  as  a  counter  electro-motive  force,  in 
others  simply  as  a  resistance,  but  in  either  case  it  can  be 
represented  in   ohms,  or   as  a  reduced   length;    but  the 
expression  of  it  is  variable,  because  it  depends  upon  the 
energy  expended  from  moment  to  moment,  and  it  must  be 
expressed  by  the  square  root  of  that  energy  involved  in 
Ohm's  formulae. 

When  all  forms  of  energy  expended  are  thus  expressed 
as  resistance  in  ohms,  the  ratio  of  useful  work  done,  to 
the  inevitable  expenditure  in  developing  and  transmitting 
the  energy  to  the  work,  is  exactly  proportional  to  the 
resistance  of  each  part  of  the  circuit. 

There  is  a  difficulty,  continues  Mr.  Sprague,  in  applying 
these  principles  to  the  illustrations  employed  by  Mr.  Sie- 
mens, in  that  we  do  not  know  what  is  meant  by  the 
resistance  of  1  ohm  at  the  point  of  work  done.  If  by 
that  is  meant  simply  the  wire  resistance  of  an  electro- 
motor or  of  a  lamp,  these  belong  to  the  side  of  energy  lost 
or  expended ;  if  the  work  to  be  done  is  not  included  in 
the  1  ohm,  then  it  would  seem  that,  as  it  would  act  as  an 


PRACTICABILITY   OF    ELECTRIC    TRANSMISSION.      37 


additional  resistance,  the  internal  resistance  of  the  generat- 
ing machine  must  be  increased  in  order  to  develop  the 
requisite  electro-motive  force. 

For  the  present  purpose,  then,  which  is  to  indicate  the 
nature  of  the  problem  and  the  difficulties  to  be  met,  rather 
than  how  to  overcome  them,  Mr.  Siemens'  actual  figures  may 
be  taken,  and  the  1  ohm  be  assumed  as  the  relative  useful 
ratio  of  the  lamp  or  motor  engine.  Here  we  meet  at  once 
the  problem,  what  is  the  work  done  in,  or  the  mechanical 
equivalent  of  an  electric  light  of,  say,  1000  candles?* 
Does  any  one  know  ?  The  problem  involves  these  simul- 
taneous measures — illuminating  power,  resistance,  and 
current.  With  batteries  of  known  electro-motive  force 
this  can  replace  the  latter  data  required.  We  have  all 
sorts  of  statements,  from  5  to  1  ohm  for  resistance,  to  the 
figures  given  by  Messrs.  Ayrton  and  Perry,  which  come 
out  as  follows  : — 


Grooves  in 
Series 
E.  M.  F.  1-8. 

Total 
E.  M.  F. 

Volts. 

Resistance. 

Current 
Webers. 

Energy  in 
Arc, 
Foot-lbs. 

Battery. 

Arc. 

Total. 

60 

108-0 

12-0 

12-0 

24-0 

5-33 

15,082 

80 

144-0 

16-0 

20-0 

36-0 

4-00 

14,157 

122 

219-6 

24-4 

30-0 

54-4 

4-04 

21,647 

Unfortunately  there  is  no  measure  of  the  light  produced 
these   three   cases.      Taking    the   common    statement 


m 


that  such  a  light  consumes  1  HP.  of  an  engine  (though 
Mr.  Siemens  states  that  his  smaller  size  converts  2  HP., 
and  gives  1250  candles)  and  take  the  resistance  as  1  ohm 
in  the  arc  and  1  •  5  in  the  machine  and  conductor ;  this 


*  As  far  as  regards  the  conductor,  it  is  immaterial  whether  the 
current  conveyed  is  utilised  to  produce  light  or  motor-power.  Hence 
the  words  of  the  argument  have  been  retained. 


38  ELECTRIC    TRANSMISSION    OF   POWER. 

gives  33,000  -f-  j—  =  13,200  feet  pounds  expended  in  the 

2 '  5 

arc,  a  very  singular  approximation  (considering  by  how 
different  a  road  it  has  been  reached)  to  the  figures  above. 
The  mechanical  equivalent  of  the  weber-ohm  current  per 
second  is  "787  foot  pound,  or  44*24  per  minute. 

13,200 

— ~—  =  289-37,   the  square  root  of  which,  17-273, 

represents  the  current  developing  13,200  foot  pounds  per 
minute  in  the  ohm  resistance,  a  useful  effect  of  0  •  4  of  the 
power  expended. 

If,  now,  100  such  lights  were  to  be  applied  to  the  same 
circuit  conditions,  it  would  be  necessary  to  put  in  circuit 
ten  in  series,  and  ten  such  series  in  multiple  arc  to  main- 
tain their  total  joint  resistance  =  1,  and  the  current  would 
have  to  be  17,273  X  10  -  172-73,  developing  100  times  as 
much  heat  in  machine  and  conductor,  and  still  expending 
0  •  6  of  the  power  in  transmission.  This  also  supposes  that 
there  is  perfect  insulation,  and  no  loss  on  the  road,  a  con- 
dition of  things  not  likely  to  be  attained  in  practice.  In 
converting  the  current  again  into  mechanical  power,  the 
0  *  4  of  power  sent  would  be  reduced  by  the  effective  ratio 
of  the  transforming  machine. 

In  regard  to  Mr.  Siemens'  proposal  to  convey  1000  HP. 
a  distance  of  30  miles  through  a  conductor  3  inches  in 
diameter,  he  says,  "  The  electrical  resistance  of  the  con- 
ductor would  be  0-18  unit,  and  supposing  that  the  total 
resistance  in  circuit  was  made  2-5  units,  which,  as  I 
before  stated,  gives  a  favourable  working  condition,  it 

0*18 

follows  that  — —  X  1000  =  72  HP.  would  be  expended  in 
2  *  5 

heating  the  conductor.  This  would  represent  about  15  Ibs. 
of  coal  per  hour,  a  quantity  quite  insufficient  to  raise  a 
mass  of  1900  tons  of  copper,  with  a  surface  of  132,000 
square  feet  to  a  sensibly-heated  condition." 


PRACTICABILITY   OF   ELECTKIC   TEANSMISSION.      39 

It  seems  from  this,  the  proposal  is  not  to  convey  1000  HP. 
but  only  so  much  as  is  possible  out  of  that  original  power. 
Then,  giving  machine  1  and  conductor  0*18  ohm  resistance, 
we  have  1  •  32  left  for  useful  work ;  so  we  divide  it : — 

1         Dynamo  machine  400  HP. 
0-18  Conductor  72    „ 

1  •  32  Engine  or  lights    528    „ 

This  latter  figure  being  reduced  in  actual  work  to  pro- 
bably 300  at  most. 

To  obtain  the  300  HP.,  then,  we  have  to  provide  : — 

1.  Machines  for  converting  the  electricity  into  300  HP. 

2.  1900  tons  of  best  copper  rod  carefully  insulated. 

3.  Machines  capable  of  converting  1000  HP.  into  electri- 

city. 

4.  Appliances  and  processes  for  getting  rid  of  400  HP. 

worth  of  heat  in  this  latter  machinery. 

Mr.  Siemens  says  he  is  convinced  that  the  sectional 
area  of  the  conductor  might  safely  be  reduced  to  2  inches, 
giving  half  the  weight  of  the  conductor ;  but  as  the  con- 
verting engines  would  probably  cost  as  much  as  gas 
engines  of  equal  power,  the  question  resolves  itself  into 
this,  is  it  better  worth  while  to  lay  down  even  950  tons 
of  copper,  and  fit  up  the  1000  H.P.  engines,  or  to  pur- 
chase the  fuel  needed  to  work  the  300  H.P.  engines  where 
they  are  to  be  used?  That  is  a  question  that  might 
receive  different  answers  in  the  mountains  of  Chili,  and 
where  coal  is  to  be  obtained  at  even  the  most  extreme 
English  prices. 

Mr.  Sprague's  views  are  practically  answered  by  the 
able  paper  presented  to  the  Franklin  Institute  by 
Professors  Thomson  and  Houston ;  the  statements  made 
as  to  the  size  and  cost  of  the  cable  that  would  be  needed 
to  convey  the  power  of  Niagara  Falls  to  a  distance  of 
several  hundred  miles  by  electricity,  having  induced  with 


40  ELECTRIC   TRANSMISSION   OF   POWER. 

the  Authors  the  hope  that  they  may  throw  light  upon  this 
interesting  subject. 

As  an  example  of  some  of  the  statements  alluded  to, 
the  following  are  cited,  viz. : — That  made  by  a  certain 
electrician,  who  asserts  that  the  thickness  of  the  cable 
required  to  convey  the  current  that  could  be  produced  by 
the  power  of  Niagara,  would  require  more  copper  than 
exists  in  the  enormous  deposits  in  the  region  of  Lake 
Superior.  Another  statement  estimates  the  cost  of  the 
cable  at  about  £12  per  lineal  foot. 

As  a  matter  of  fact,  however,  the  thickness  of  the  cable 
required  to  convey  such  power  is  of  no  particular  moment, 
and  the  Professors  state  that  it  is  possible,  should  it  be 
deemed  desirable,  to  convey  the  total  power  of  Niagara 
a  distance  of  500  miles  or  more  by  a  copper  cable  not  exceeding 
one-half  of  an  inch  in  thickness.  This,  however,  is  an 
extreme  case,  and  the  exigencies  of  practical  working 
would  not  require  such  restrictions  as  to  size.  The  follow- 
ing considerations  will  elucidate  this  matter: — Suppose 
two  machines  connected  by  a  cable  of,  say,  1  mile  in 
length.  One  of  these  machines,  for  example  A,  is  pro- 
ducing current  by  the  expenditure  of  power ;  the  other 
machine,  B,  used  as  an  electrical  motor,  is  producing 
power  by  the  current  transmitted  to  it  from  A  by  the 
cable  C.  The  other  terminals,  x  and  y,  are  either  put  to 
earth  or  connected  by  a  separate  conductor. 

Let  us  suppose  that  the  electro-motive  force  of  the 
current  which  flows  is  unity,  since,  by  the  revolution  of 
B,  a  counter  electro -motive  force  is  produced  to  that  of  A, 
the  electro-motive  force  of  the  current  that  flows  is  mani- 
festly the  difference  of  the  two.  Let  the  resistance  of  A 
and  B  together  be  equal  to  unity,  and  that  of  the  mile  of 
cable  and  connections  between  them  the  0  •  01  of  this  unit. 

TT  1 

Then  the    current  which  flows  will  be  C  =  =   = 


E        1-01 
If,  now,  an  additional  machine  A'  and  an  additional  motor 


PRACTICABILITY   OF   ELECTRIC   TRANSMISSION.       41 

B',  and  an  additional  mile  of  cable  be  introduced  into  the 
above  circuit,  the  electro-motive  force  will  be  doubled, 
and  the  resistances  will  be  doubled,  the  current  strength 

E  1  +  1  2 

remaining  the  same  as  C     =  g  ==    JTQI  +  I.OI  =  ^02* 

Here  it  will  be  seen  that  the  introduction  of  the  two 
additional  machines  A'  B'  has  permitted  the  length  of  the 
cable,  C,  to  be  doubled  without  increasing  the  strength  of 
the  current  which  flows,  and  yet  allowing  the  expenditure 
of  double  the  power  at  A  A',  and  a  double  recovery  at 
B  B'  of  power,  or,  in  other  words,  a  double  transmission  of 
power  without  increase  of  current. 

Increase  now  the  number  of  machines  at  A  to,  say,  one 
thousand,  and  one  of  those  at  B  in  like  proportion,  and 
the  distance  between  them,  or  the  length  of  the  cable,  one 
thousand  times,  or  in  the  case  we  have  supposed  make  it 
one  thousand  miles,  its  diameter  remaining  the  same,  then, 
although  the  same  current  will  flow,  yet,  we  have  a  thousand 
times  the  expenditure  of  power  at  one  end  of  the  cable  and  a 
thousand-fold  recovery  at  the  other  end,  without  increase  of 
current.  And  the  same  will  be  true  for  any  other  pro- 
portion. 

Since  the  electro-motive  force  is  increased  in  proportion 
to  the  increase  of  power  transmission,  the  insulation  of 
the  cable  and  machines  would  require  to  be  proportion- 
ally increased. 

As  an  example  it  may  be  mentioned  that  a  dynamo- 
electric  machine  used  for  A  may  have  a  resistance  of,  say, 
40  ohms  and  produce  an  electro-motive  force  of,  say,  400 
volts.  Such  a  machine  might  require  from  three  to  five 
horse-power  when  used  in  connection  with  a  suitable  motor 
B,  for  recovery  of  the  power  transmitted. 

If  the  resistance  of  the  motor  B  be,  say,  60  ohms,  and 
the  cable  transmitting  the  currents  a  distance  of  1  mile 

be  1  ohm,  then  the  current  C  =  ^-—  =  — . 


42  ELECTRIC   TRANSMISSION   OF  POWER. 

If,  now,  1000  machines  and  1000  motors  and  1000 
miles  of  cable,  each  of  the  same  relative  resistances, 

1000  X  400 

be  used  the  current  C  =  -Z-T^TT—      ;r-»  which  has  mani- 

1000  x  101 

festly  the  same  value  as  before.  If  the  supposition  of  the 
power  used  to  drive  one  machine  be  correct,  then  from 
3000  to  5000  HP.  would  be  expended  in  driving  the 
machines,  and  possibly  about  50  per  cent,  of  this  amount 
recovered.  Then  we  have  from  1500  to  2000  HP.  con- 
veyed a  distance  of  1000  miles.  What  diameter  of  copper 
cable  will  be  required  for  such  transmission  ?  Since  this 
cable  is  supposed  to  have  the  resistance  of  1  ohm  to  the 
mile,  calculation  would  place  the  requisite  thickness  at 
about  J  inch.  If,  however,  the  distance  be  only  500  miles, 
then  the  resistance  per  mile  may  be  doubled,  or  the 
section  of  the  cable  be  decreased  one  half,  or  its  diameter 
will  be  less  than  one-fifth  of  an  inch. 

For  the  consumption  of  1,000,000  HP.  a  cable  of  about 
3  inches  in  diameter  would  suffice  under  the  same  condi- 
tions. However,  by  producing  a  much  higher  electro- 
motive force,  the  section  of  the  cable  could  be  propor- 
tionally reduced  until  the  theoretical  estimates  given  in 
the  preceding  lines  might  be  fulfilled.  The  enormous 
electro-motive  force  required  in  the  above  calculation 
would,  however,  necessitate  such  perfect  insulation  of  the 
cable  that  the  practical  limits  might  soon  be  reached.  The 
amount  of  power  required  to  be  conveyed  in  any  one 
direction  would,  of  course,  be  dependent  upon  the  uses 
that  could  be  found  for  it,  and  it  is  hardly  conceivable 
that  any  one  locality  could  advantageously  use  the 
enormous  supposed  power  we  have  referred  to. 

Stripped  of  its  theoretical  considerations,  the  important 
fact  still  remains,  that  with  a  cable  of  very  limited  size 
an  enormous  quantity  of  power  may  be  transferred  to 
considerable  distances.  The  burning  of  coal  in  the  mines, 
and  the  consequence  of  the  power  generated  by  the  flow 


PRACTICABILITY  OF   ELECTRIC   TRANSMISSION.       43 

of  rivers,  may  therefore  be  regarded  as  practicable, 
always,  however,  remembering  that  a  loss  of  about  50  per 
cent,  will  be  almost  unavoidable. 

In  a  subsequent  series  of  experiments,  details  of  which 
are  unpublished,  the  Professors  Thomson  and  Houston 
have  succeeded  in  transmitting  considerable  power  through 
a  wire  only  0  •  004  inch  in  diameter.  Sir  William  Thomson 
has  made  statements  that  are  in  general  accordance  with 
these  views.  Mr.  Siemens  has  remarked  that  the  electrical 
transmission  of  power,  although  new  and  untried,  is  one 
of  considerable  interest,  and  an  amount  of  from  40  to 
50  per  cent,  is  recovered  at  the  end  of  the  line.  By 
putting  one  machine  to  work  with  an  expenditure  of,  say, 
3  HP.,  a  power  could  be  produced  and  utilised  at  a  dis- 
tance not  exceeding  half  a  mile  or  a  mile,  according  to  the 
size  and  length  of  the  conductor,  equal  to  nearly  one-half 
that  amount.  If  at  certain  stations  100  HP.  were  so 
exerted,  it  would  be  possible  to  distribute  over  a  town 
power  which  would  be  exceedingly  convenient  and  free 
from  the  dangers  and  troubles  attending  caloric  motors, 
and  with  an  expenditure  of  fuel  certainly  not  greater, 
because,  although  perhaps  only  40  per.  cent,  of  the  power 
exerted  at  the  central  station  was  actually  obtained  at  the 
further  station,  it  was  nevertheless  obtained  at  a  very  low 
rate.  A  100-HP.  engine,  economically  constructed,  would 
produce  1  HP.  with  less  than  3  Ibs.  of  coal,  whereas  a 
small  motor  of  2  or  3  HP.  would  consume  probably  6  to 
8  Ibs.  of  coal  per  hour.  Bearing  that  difference  in  mind, 
the  magneto-electric  machine  would  be  an  economical  one. 
How  far  the  principle  would  be  applicable  ultimately  for 
the  utilisation  of  such  natural  forces  as  water-power  from 
a  distance,  remains  to  be  seen.  The  difficulty  is  in  regard 
to  the  length  of  the  electrical  conductor.  Its  resistance 
increased  in  the  ratio  of  its  length ;  and  as  the  increased 
resistance  would  mean  loss  of  useful  effect  in  the  same 
proportion,  it  would  be  necessary  to  double  the  area  of 


44  ELECTRIC   TRANSMISSION   OF   POWER. 

the  electric  conductor  in  doubling  its  length,  in  order  to 
maintain  the  same  ratio  of  efficiency ;  but,  if  that  were 
done,  the  resistance  might  be  increased  to  many  miles, 
and,  he  believed,  profitably,  without  further  loss  of  power. 

Professors  Houston  and  Thomson  have,  however,  shown 
as  noted  in  the  preceding  lines  how  this  loss  is  to  be 
avoided. 

In  order  to  get  the  best  effect  out  of  a  dynamo-electric 
machine,  there  should  be  an  external  resistance  not  ex- 
ceeding the  resistance  of  the  wire  in  the  machine. 
Hitherto,  Mr.  Siemens  continues,  it  has  been  found  not 
economical  to  increase  the  resistance  in  the  machine  to 
more  than  1  ohm,  otherwise  there  was  a  loss  of  current 
through  the  heating  of  the  coil.  If,  therefore,  there  was 
a  machine  with  1  ohm  resistance,  there  ought  to  be  a  con- 
ductor transmitting  the  power  to  the  electro-magnetic 
engine  not  exceeding  1  ohm.  If,  instead  of  going  1  mile, 
it  was  desired  to  go  2  miles,  it  would  be  necessary  first  of 
all  to  employ  a  conductor  twice  the  length  ;  but  that  con- 
ductor would  give  2  ohms  resistance,  and  would  therefore 
destroy  much  of  the  effect.  To  bring  it  back  to  1  ohm 
resistance,  it  would  be  necessary  to  put  down  a  second 
wire,  or  to  double  the  area  of  the  first,  and  in  that  case 
there  would  be  a  wire  of  twice  the  length  and  twice  the 
area,  therefore  four  times  the  weight  and  four  times  the 
cost.  That  pointed  to  an  increase  in  the  cost  and  in  the 
weight  of  the  conductor  in  the  square  ratio  of  the  distance. 
Having  twice  the  area  to  deal  with,  a  second  generator 
could  be  put  on,  and  electricity  enough  to  work  two 
machines  could  be  sent  through  the  double  area  to  a 
double  distance.  The  moment  that  was  done,  the  con- 
ductor was  increased,  for  the  power  was  transmitted  only 
in  the  proportion  of  the  increase  of  the  length  ;  but  that 
was  not  enough.  The<  electric  conductor  did  not  resist 
the  motion  of  electricity  in  the  same  manner  as  a  pipe 
resisted  the  flow  of  liquid  through  it,  but  an  ohm's 


PRACTICABILITY   OF   ELECTRIC   TRANSMISSION.      45 

resistance  was  an  ohm's  resistance  for  a  larger  as  well  as 
for  a  smaller  current  flowing  through  it,  which  resistance 
was  only  increased  by  a  rise  of  temperature  in  the  con- 
ductor. This  rise  of  temperature  was  kept  down  by 
dissipation  of  heat  from  the  conductor ;  or,  considering 
that  the  longer  and  doubled  conductor  would  possess  four 
times  the  amount  of  surface  for  the  dissipation  than  the 
single  and  short  conductor,  it  would  be  capable  of  trans- 
mitting four  times  the  amount  of  electric  current.  It 
might,  therefore,  be  said  that  it  was  no  dearer  to  transmit 
electro-motive  force  to  the  greater  than  to  the  smaller 
distance,  as  regarded  weight  and  cost  of  conductor,  a 
result  which  seemed  startling,  but  which  he  nevertheless 
ventured  to  put  forward  with  considerable  confidence. 
In  uniting  the  two  longer  conductors  into  one,  the  surface 
would,  however,  be  increased  only  in  the  ratio  of  ,J  2  : 1 ; 
therefore  the  relative  transmitting  power  between  the 
longer  and  shorter  conductor  would,  strictly  speaking,  be 
increased  in  the  ratio  of  1:2^2,  or  1:2*  83,  and  the 
longer  conductor  would  be  dearer  than  the  shorter  per 
unit  of  electro-motive  force  transmitted  in  the  proportion 
of  4:2-83. 

Sir  William  Thomson  has  remarked  that  the  question 
of  the  heat  developed  in  the  wire  was  the  fundamental 
question  with  reference  to  the  quantity  of  metal  required 
to  communicate  the  effect  to  a  distance.  The  most  prac- 
tical way  of  producing  the  result  would  be  to  put  the 
wire  in  the  shape  of  a  copper  tube.  Having  a  copper  tube, 
with  a  moderate  amount  of  copper  in  its  sectional  area, 
and  a  current  of  water  flowing  through  it  with  occasional 
places  to  let  it  off,  and  places  to  allow  water  to  be 
admitted  for  the  purpose  of  cooling,  there  would  be,  with- 
out any  injury  to  the  insulation,  a  power  of  carrying  off 
heat  practically  unlimited.  He  believed  that  with  an  ex- 
ceedingly moderate  amount  of  copper,  it  would  be  possible 
to  carry  the  electric  energy  to  a  distance  of  several 


46  ELECTRIC   TRANSMISSION   OF  POWER. 

hundred  miles.  The  economical  and  engineering  moral  of 
the  theory  appeared  to  be  that  towns  henceforth  would  be 
lighted  by  coals  burned  at  the  pit's  mouth,  where  it  was 
cheapest.  The  carriage  expense  of  electricity  was  nothing, 
while  that  of  coal  was  sometimes  the  greater  part  of  its 
cost.  The  dross  at  the  pit's  mouth,  which  was  formerly 
wasted,  could  be  used  for  working  dynamo-engines  of  the 
most  economical  kind.  Nothing  could  exceed  the  practical 
importance  of  this  fact.  The  power  transmissible  by  these 
machines  was  not  simply  sufficient  for  working  sewing- 
machines  and  turning  lathes,  but  by  putting  together  a 
sufficient  number  any  amount  of  HP.  might  be  developed. 
Taking  the  case  of  the  machines  required  to  develop  1000 
HP.,  he  believed  it  would  be  found  comparable  with  the 
cost  of  a  1000  HP.  engine;  and  he  need  not  point  out 
the  vast  economy  to  be  obtained  by  the  use  of  such  a  fall 
as  that  of  Niagara,  or  the  employment  of  waste  coal  at  the 
pit's  mouth. 


EFFICIENCY   OF    COUPLED    MACHINES.  47 


CHAPTEE   VII. 

EFFICIENCY   OF   COUPLED   MACHINES. 

As  regards  the  efficiency  of  the  system  comprising  two 
machines,  the  following  quotation  from  a  paper  read  by 
the  Author  before  the  Institution  of  Civil  Engineers, 
1878  (for  which  the  Telford  Medal  was  awarded),  will 
fully  elucidate  this  point : — 

The  means  at  present  employed  for  the  transmission  of 
power  to  a  distance  are  well  known.  In  adding  to  the 
list  it  may  be  well  to  point  out  that  between  the  use  of 
electricity,  when  obtained  from  a  voltaic  battery,  and 
conveyed  to  an  electro-magnetic  motor  by  conducting 
wires,  and  the  employment  of  dynamo-machines,  there  is 
just  the  difference  that  results  in  obtaining  the  electric 
light  by  a  Grove  or  a  Bunsen  battery,  and  in  taking  the 
light  from  the  current  produced  by  the  dynamo-machine. 
In  the  one  case  an  expensive  chemical  action  is  converted 
into  force ;  in  the  other,  the  force  produced  by  a  steam  or 
other  economical  motor  is  transmitted.  With  the  electro- 
magnetic motor  the  system  is  generative ;  with  the 
dynamo-machine,  the  current  acts  merely  as  a  means  of 
transmitting  power  produced  by  an  independent  motor. 
In  point  of  fact,  this  independent  motor  may  be  a  natural 
source  of  power,  such  as  the  fall  of  water,  the  utilisation 
of  the  product  of  oil  wells,  with  prime-movers  situated  at 
these  wells,  etc. 

The  limit  set  by  distance  to  the  transmission  of  power, 
by  means  at  present  adopted,  has  been  comparatively 
narrow.  Hydraulic  power  has  been  the  most  adaptable, 
with,  however,  several  important  disadvantages.  Although 


48  ELECTRIC   TRANSMISSION   OF    POWER. 

electricity  as  a  means  of  transmission  is  also  limited  by 
the  distance  to  be  traversed,  the  limit  is  in  this  case  much 
more  extensible,  and  under  favourable  instances  practically 
disappears.  The  limit  is  dependent  upon  the  quantity  of 
electricity  that  can  be  conveyed  by  the  conductor,  since 
mechanical  efficiency  depends  upon  the  magnetic  energy. 

For  the  transmission  of  power,  say  from  a  steam  or 
water  motor  initially,  the  following  system  is  adopted : 
First,  a  strap  or  belt  from  the  motor  is  carried  to  the 
pulley  of  the  driving  dynamo-electric  machine  which 
generates  the  current.  By  leading  wires  of  the  required 
length,  the  electrical  current  generated  in  the  first 
machine  is  conveyed  to  the  terminals  of  a  second  and 
precisely  similar  machine.  Thus  the  first  machine 
generates  the  current  which  is  utilised  in  imparting 
motion  to  the  second  machine.  It  remains  to  review 
the  probable  efficiency  of  such  a  system.  This  subject 
has  been  treated  in  its  mathematical  relations  by  M. 
Mascart  in  the  '  Journal  de  Physique.' 

It  is  well  known  that  all  magneto-electric  machines, 
when  set  in  motion  by  a  current,  induce  in  themselves,  as 
electrical  systems,  currents  opposing  the  motive  current. 
For  example,  when  a  current  from  some  source  is  directed 
into  the  coils  of  a  dynamo-machine,  the  coil  commences  to 
revolve.  Immediately  it  commences  to  revolve,  it  also 
begins  to  act  as  a  generator,  and  sets  up  a  current  which 
is  opposite  in  direction  to  the  motive  current,  and  sub- 
tractive  from  the  strength  of  the  latter.  The  current- 
strength  from  the  source  is,  therefore,  at  a  maximum  when 
the  second  machine,  or  that  driven  by  the  current,  is  at 
rest.  From  consideration  it  is  easily  obtained  that  the 
greatest  work  is  to  be  yielded  by  the  second  machine 
when  the  strength  of  the  current  given  by  the  first 
machine,  or  source,  has  been  reduced  to  one-half  by  the 
induced  current  from  the  second  machine.  With  these 
machines  it  has  been  generally  found  that  the  current- 


EFFICIENCY  OF   COUPLED  MACHINES. 


49 


strength   is   proportional  to   the  velocity  or   number   of 
revolutions  of  the  cylinder ;  so  that,  supposing  two  equal 


FIG.  19. 

•nOO  Rex*   of 


FIG.  20. 

tlOO  Rou*    of  1*6  Kachinjer 

/^ 

"^ 

\ 

/ 

\ 

/ 

/ 

00                 *00                  SOO                 SOO                  TOO                  SCO                  SOO                   WOO               TOO                  12C 
Rar*    of    ""•"*'    Machine 

machines  arranged  for   the   transmission   of  power,  the 
amount  of  work  reclaimable  from  the  second  machine  will 

E 


50 


ELECTRIC  TRANSMISSION  OF  POWER. 


be  50  per  cent,  of  that  employed  upon  the  first,  and  the 
number  of  revolutions  of  the  armature  of  the  second 
machine  corresponding  to  the  maximum  of  work  reclaimed 
will  be  half  the  number  made  by  the  first. 

Figs.  19  to  21  show  curves  drawn  through  six  points 
from  results  actually  obtained.  The  revolutions  of  the 
cylinder  of  the  second  machine  are  represented  as  abscissae 

FIG.  21. 

1300    Rjevf    of   V*> 


, 

^ 

. 

L^-- 

\ 

/ 

^ 

^ 

1 

X 

*>                 400                   600                  600                   TOO                   SCO                 9OO           '       10 

OO             rn 

'o           ma 

Rev*     of    2~ 

and  the   work   reclaimed   as   ordinates.     The   numerical 
values  are  given  in  the  following  table : — 

KESULTS  OF  EXPERIMENTS  WITH  DYNAMO-MACHINES  FOR  THE  TRANS- 
MISSION OF  POWER  BY  THE  ELECTRIC  CURRENT. 


Fig.  19. 

Fig.  20. 

Fig.  21. 

Machine  A,  at  1100  Revo- 

Machine A,  at  11  00  Revo- 

Machine A,  at  1400  Revo- 

lutions Driving  C. 

lutions  Driving  B. 

lutions  Driving  B. 

Revolutions 
ofC. 

Per  cent,  of 
Work  Re- 
claimed. 

Revolutions 
ofB. 

Per  cent,  of 
Work  Re- 
claimed. 

Revolutions 
ofB. 

Per  cent,  of 
Work  Re- 
claimed. 

1,008 

27 

884 

34 

1,199 

39 

730 

36 

808 

43 

1,031 

44 

584 

38 

767 

44 

863 

48 

501 

39 

625 

45 

691 

49 

420 

37 

481 

39 

500 

37 

359 

35 

385 

32 

•• 

•• 

EFFICIENCY   OF   COUPLED   MACHINES.  51 

The  departures  from  the  theoretical  values  are  somewhat 
marked,  but  are  within  the  limits  of  error  that  occur  with 
this  class  of  measurements,  made  with  no  great  attempt 
at  accuracy. 

In  order  to  ascertain  the  effects  of  resistance  in  the 
circuit  connecting  the  driving  and  driven  engines,  two 
machines  were  connected  by  leading  wires,  having  resist- 
ance of  J  unit,  1  unit,  and  1J  unit  respectively.  The 
machines  were  two  of  the  smallest  Siemens  type,  and  gave 
without  inserted  resistance  an  efficiency  of  44  per  cent. ; 
with  %  unit  resistance  added  to  the  circuit  the  efficiency 
was  reduced  to  38  per  cent.,  giving  a  loss  of  6  per  cent. ; 
with  1  unit  of  added  resistance  the  efficiency  fell  to  32  per 
cent.,  giving  a  loss  of  12  per  cent. ;  and  with  Ij  unit  added 
resistance  the  efficiency  was  26  per  cent.,  giving  a  loss 
of  18  per  cent.  The  experiments  clearly  proved  that  the 
loss  of  efficiency  is  proportional  to  the  added  resistance. 

With  a  machine  having  O'Oo  unit  resistance,  a  current 
of  5  webers  through  one  ohm  has  been  obtained,  with  an 
expenditure  of  2  HP.  This  gave  a  current  of  which  the 
mechanical  value,  when  the  machine  was  connected  to  a 
precisely  similar  machine,  was  56,000  foot-lbs.,  with  the 
second  machine  at  rest;  and  a  resultant  current  of 
29,000  foot-lbs.  with  the  second  machine  in  motion,  the 
HP.  expended  being  maintained  constant.  The  work  re- 
claimed, measured  on  the  dynamometer,  was  48  per  cent., 
closely  agreeing  with  the  efficiency  of  one-half.  As  to 
the  effect  of  circuit  resistance  on  the  transmission  of  power 
in  the  instance  quoted,  the  addition  of  1 J  unit  resistance 
reduced  the  efficiency  to  26  per  cent,  with  the  particular 
machines  employed;  but  if  convolutions  of  wire  were 
added  to  the  cylinder  of  the  machine  the  efficiency  would 
again  attain  its  maximum.  It  should  be  noted'  that  the 
theoretical  efficiency  of  50  per  cent,  is  referred  to  the  use 
of  two  equal  and  similar  machines,  one  used  as  the  driving, 
the  other  as  the  driven  machine.  It  is  quite  probable 

E  2 


52  ELECTRIC   TRANSMISSION  OF  POWER. 

that  a  larger  percentage  of  work  reclaimed  might  be 
attained  by  some  other  arrangement  of  machines.  By 
driving  one  machine  by  two  others  coupled  in  series,  the 
results  of  three  readings  gave :  speed  of  small  machines, 
1060  revolutions;  speed  of  medium  machine,  1820  revo- 
lutions. The  medium  machine  driven  by  one  small 
machine  gave  the  following  results,  taken  from  three 
readings :  speed  of  small  machine,  1060  revolutions ;  speed 
of  medium  machine,  780  revolutions.  It  would  thus  be 
seen  that  the  speed  of  the  medium  machine  had  been 
rather  more  than  doubled  by  driving  it  from  two  machines 
coupled  in  series.  The  best  conditions  for  work  admitted 
of  direct  proof.  Two  equal  machines  being  employed,  and 
a  galvanometer  put  in  circuit  between  them,  the  deflec- 
tions showed  that  when  the  second  machine  was  at  rest, 
the  current  was  of  twice  the  intensity  that  occurred  when 
the  second  machine  was  giving  out  its  best  work. 

M.  Mascart  has  shown  that  if  the  number  of  revolutions 
of  the  first  machine  were  kept  constant,  the  greatest  effi- 
ciency would  be  attained  when  the  number  of  the  revolu- 
tions of  the  second  machine  were  nearly  equal  to  unity. 
But  he  has  also  proved  that  when  the  greatest  amount  of 
power  was  given  off  by  the  second  machine,  it  would  make 
half  the  number  of  revolutions  of  the  first  machine,  and 
then  the  first  machine  would  require  half  the  power  to 
drive  it  which  was  required  when  the  second  machine  was 
standing,  and  of  that  power  one  half  would  be  transmitted 
by  the  second  machine.  This  is  a  very  different  thing  from 
the  conclusion  that  the  maximum  efficiency  was  one  half. 

In  some  experimental  researches  on  magneto-electric 
machines,  MM.  Mascart  and  Angot,  in  the  '•Journal  de 
Physique,'  vol.  vii.  p.  78,  investigate  the  reaction  of  the 
magnets  and  the  electro-magnets.  Previous  considerations 
in  a  former  article*  by  these  authors,  give  only  a  first  ap- 


Vide  Minutes  of  Proceedings  Inst.  C.E.,  vol.  L.,  p.  302. 


EFFICIENCY   OF    COUPLED   MACHINES.  53 

proximation  to  the  action  of  machines  containing  magnets 
or  electro-magnets.  It  has  been  supposed  that  the  mag- 
netism of  permanent  magnets  is  invariable,  and  that  that 
of  electro-magnets  depends  only  upon  the  intensity  of 
the  currents  by  which  they  are  surrounded ;  but  there 
exist  between  the  magnets  and  the  currents  reactions 
that  may  greatly  modify  the  results.  Electro-dynamic 
machines  which  include  neither  magnet  nor  soft  iron 
give  rise  to  no  new  correction,  the  time  necessary  for 
the  manifestation  of  the  electro-dynamic  forces  being 
inappreciable. 

In  magnetic  machines  of  the  second  type  the  effective 
magnetism  of  the  permanent  magnets  is  changed  in  a 
complex  manner  by  the  influence  of  the  bobbins.  If  it 
be  admitted  that  the  variation  of  the  magnetism  of  the 
magnets  is  proportional  to  the  magnetic  power  of  the 
bobbins,  which  is  in  direct  ratio  to  the  intensity  of  the 
current,  it  is  to  be  seen  that  the  magnetism  of  the  magnets 
will  be  increased  when  they  exercise  an  attraction  between 
the  two  systems,  and  that  it  will  be  diminished  in  the 
case  of  repulsion.  The  diminution  of  repulsive  force  will 
be  greater  than  the  increase  of  attractive  force,  since  the 
magnets  may  be  supposed  to  be  in  a  condition  bordering 
upon  saturation ;  there  will  result  from  this  fact  a  slight 
diminution  of  work,  and  this  may  be  represented  by  a 
term  proportional  to  the  square  of  the  intensity  of  the 
current.  The  equations  *  then  become  for  the  motor 
machine, 

K  =  NH  =  NI(A-BI) 

E  = 


*  I  and  i  are  current  intensities ;  E0  primary  electro-motive  force ; 
E  contrary  electro-motive  force ;  R  total  resistance ;  N  and  n  number  of 
revolutions  in  the  two  machines  in  corresponding  cases.  K  is  the  me- 
chanical work  in  time  di.  The  other  relations  are  explained  in  the  text. 


54  ELECTRIC   TRANSMISSION   OF   POWER. 

Whence  is  deduced, 


instead  of  E  =  N  A.  The  electro-motive  force  of  induc- 
tion, for  a  given  velocity,  is  as  much  weaker  as  that  of 
the  battery  is  stronger.  The  machine  left  to  itself  has 
still  a  velocity,  the  limit  of  which  is  given  by  the  condi- 
tion 1  =  0,  which  is 

A 

as  if  the  reaction  had  not  been  taken  into  account.  The 
efficiency  is  diminished,  because  it  has  for  expression, 


_  E__  NA         AB 

E°       E°  T       N  - 
E 

To  calculate  the  coefficients  A  and  B  the  limit  of  velo- 
city N0  of  the  motor  machine  must  be  determined,  whence 
is  deduced 

A-E» 
N.' 

as  measure  for  the  efficiency  for  a  given  velocity ;  thus 
the  equation 

B 


obtains,  whence  is  deduced 

N 

iv.  ~r 
B  =  E 


EFFICIENCY   OF   COUPLED   MACHINES.  55 

The  limit  of  velocity  N0  is  easily  obtained  by  experi- 
ment, since  it  is  proportional  to  the  electro -motive  force 
of  the  battery  employed,  which  may  be  chosen  as  weak  as 
desired. 

When  the  machine  is  employed  as  electro-motor,  the 

condition  of  production    2  —  >  R  is  always  realised  for 
a  very  weak  current,  and  equilibrium  exists  when 


or 

A  n  A  n  A 


B  B  +  .B       Jt  F 

n  xt 

The  apparatus  behaves  as  a  battery,  the  electro-motive 
force  of  which  is  proportional  to  the  velocity,  with  the 
conditions  of  adding  to  the  actual  resistance  a  fictitious 
resistance  itself  proportional  to  the  velocity.  The  inten- 
sity will  then  have  a  limiting  value  given  by  the  equation, 

_A. 
=  B' 

In  magneto-electric  machines,  that  is  to  say  with  fixed 
and  moving  electro-magnets,  the  influence  of  the  wires  of 
a  system  of  bobbins  on  the  opposed  electro-magnets  gives, 
as  in  the  preceding,  an  increase  of  attractive  forces  and  a 
greater  diminution  of  repulsive  forces,  which  again  intro- 
duces into  the  work  a  negative  variation  proportional  to 
the  magnetism  and  to  the  intensity  of  the  current  that 
may  be  considered  comprised  in  the  term  C^  M  I2.  On  the 
other  hand,  the  reciprocal  influence  of  the  electro-magnets 
gives  also  a  diminution  of  work,  which  is  sensibly  propor- 
tional to  the  square  of  the  magnetisation,  and  may  be 
comprehended  in  the  term  C2  M2  I2,  so  that  there  will  be 


56  ELECTRIC   TRANSMISSION  OF  POWER. 

nothing  to  modify  the  theory.  The  reaction  which  is 
weak  in  the  machines  of  the  second  type,  plays  on  the 
contrary  an  important  part  in  composite  machines  consist- 
ing of  magnets  and  electro-magnets.  If  it  be  considered 
that  the  magnetism  of  fixed  magnets  is  modified  by  a 
quantity  proportional  to  the  magnetisation  of  the  electro- 
magnets, there  results  a  diminution  of  work  proportional 
to  the  square  of  magnetisation,  or  to  M2  I2. 
The  efficiency  is 

T_  2 


JE  _  N  (A  4-  A!  M)          A+AiM     R 
"  E;  ~          ~E7~  A2M2 

~K~ 

If  the  current  is  sufficiently  weak,  so  that  the  coefficient 
M  has  the  constant  value  M0,  it  becomes 


an  expression  of  the  same  form  as  for  machines  of  the 
second  type  of  magneto-electric  machines.  The  greater 
number  of  electric  motors  enter  into  the  category,  because 
they  are  nearly  always  formed  of  two  systems  of  electro- 
magnets— or,  what  is  the  same,  of  a  system  of  fixed  electro- 
magnets, and  of  movable  pieces  of  soft  iron.  In  these 
machines  work  has  for  expression, 

K  =  NH  =  NP  (C  +  d  M-f  C2  M2). 

If  the  intensity  is  feeble  the  parenthesis  may  be  repre- 
sented by  a  constant  A,  and 

K  =  N  A  I2, 

and  the  electro-motive  force  of  induction  is 
E  =  N  A  I. 


EFFICIENCY   OF   COUPLED   MACHINES.  57 

For  the  other  part, 

I  K  =  E0  -  E  =  K  I0  -  N  A  I, 

whence  is  deduced 


The  Gramme  machine  with  electro-magnets  enters  into 
the  same  type  in  theory,  but  entirely  differs  from  the 
preceding  in  construction.  This  machine  the  Authors 
have  studied  as  an  electro-motor  only.  The  resistance  of 
the  machine  is  not  constant,  because  the  commutator 
brush  communicates  successively  with  the  different  bobbins 
of  the  ring,  but  does  not  vary  more  than  T^-g- ;  the  mean 
is  1*104  ohm.  The  Authors  have  added  successively 
exterior  resistances  to  the  amount  of  200  ohms,  and  have 
varied  the  speed  from  a  quarter  of  a  revolution  to  nineteen 
revolutions  per  second.  It  should  be  remarked  that  this 
enormous  speed  can  be  obtained  on  very  resistant  circuits 
only,  because  the  intensity  increases  so  rapidly  that  with 
a  shorter  circuit  all  the  disposable  power  of  the  motor, 
which  equalled  5  HP.,  could  not  be  utilised.  All  the 
quantities  are  reduced  into  absolute  units  (webers),  and 
the  resistance  expressed  in  ohms.  The  phenomena  are 
regular  when  the  resistance  does  not  exceed  10  ohms,  nor 
the  speed  of  the  machine  ten  revolutions  per  second. 
Thus,  if  the  quantity  is  inferior  to  0*08  weber,  it  is 
proportional  to  the  speed,  and  in  inverse  ratio  to  the  total 
resistance  of  the  circuit.  For  larger  quantities  the  con- 
stant has  for  expression  — ,  which  depends  only  upon 

the  intensity  of  the  current.     This  result  accords  with 
theory.     The  electro-motive  force  is 

n  i  (C  +  Cx  M  +  C2  M2), 


58  ELECTKIC   TRANSMISSION  OF   POWER, 

which  gives 


The  values  of  -  —  increasing  nearly  proportionally  to  the 

quantity,  calculations  can  be  effected  by  the  following 
empirical  formula, 

—  =  0-286  +  0-4f, 
n 

where  f  is  the  quantity  of  current,  R  the  resistance  of  the 
whole  circuit,  and  n  the  number  of  revolutions  of  the 
Gramme-armature. 


COMPAKATIVE  EFFICIENCY  OF  VARIOUS  MACHINES.     59 


CHAPTEE  VIII. 

COMPARATIVE   EFFICIENCY   OF   VARIOUS   MACHINES. 

NOTHING  can  be  done  in  the  inter-comparison  of  any 
natural  force  until  accurate  measurements  have  been 
made.  For  those  measurements  we  are  indebted  to  a  great 
extent  to  the  labours  of  the  committee  on  dynamo-elec- 
tric machines  formed  by  the  Franklin  Institute,  and  to 
Professors  Houston  and  Thomson's  report  as  to  the 
ratio  of  efficiency  in  the  conversion  of  motive-power  into 
electricity. 

In  entering  this  comparatively  new  field  of  research, 
peculiar  difficulties  occurred,  owing  to  conditions  that  do 
not  exist  in  the  various  forms  of  batteries  used  as  sources 
of  electrical  power.  In  many  battery  circuits  a  high 
external  resistance  may  be  employed,  and  the  electro- 
motive force  remains  comparatively  constant,  while  in 
dynamo-electric  machines,  in  which  the  reaction  principle 
is  employed,  the  introduction  of  a  very  high  external 
resistance  into  the  circuit  must  be  necessarily  attended 
by  decided  variations  in  the  electro-motive  force  due  to 
changes  in  the  intensity  of  the  magnetic  field  in  which 
the  currents  have  their  origin.  Moreover,  a  considerable 
difficulty  is  experienced  in  the  great  variations  in  the 
behaviour  of  these  machines  when  the  resistance  of  the 
external  work  is  changed.  Changes  due  to  loss  of  con- 
ductivity by  heating,  also  take  place  in  the  machine 
itself.  These  variations  are  also  attended  by  changes  in 
the  power  required  to  drive  the  machine,  and  in  the  speed 
of  running,  which  again  re-act  on  the  current  generated. 
These  are  certain  normal  conditions  in  the  running  of 


60  ELECTRIC   TRANSMISSION  OF  POWER. 

dynamo-electric  machines  under  which  all  measurements 
can  be  made,  viz. : — 

The  circuit  must  be  closed,  since,  on  opening,  all  elec- 
trical manifestations  cease. 

The  speed  of  the  machine  must  be,  as  nearly  as  possible, 
constant. 

The  power  required  to  maintain  a  given  rate  of  speed 
must  be,  as  nearly  as  possible,  constant. 

The  machines  submitted  to  the  Committee  for  determi- 
nation were  as  follows,  viz. : — 

1.  Two   machines   of  different   size,  and  of  somewhat 
different    detailed   construction,   built    according   to   the 
invention  of  Mr.  C.  F.  Brush,  and  styled  respectively  in 
the  same  report  as  A1,  the  larger  of  the  two  machines,  and 
A2,  the  smaller. 

2.  Two     machines,     known     as     the    Wallace-Farmer 
machines,  differing  in  size  and  in  minor  details  of  con- 
struction, and  designated  respectively  as  B1,  the  larger  of 
the  two,  and  B2,  the  smaller.     In  the  case  of  the  machine 
B1,  the  experiments  were  discontinued  after  the  measure- 
ment   of    the   resistances   was   made,   insufficient   power 
being  at  disposal  to  maintain  the  machine  at  its  proper 
rate  of  speed. 

3.  A  Gramme  machine  of  the  ordinary  construction. 
All  the  above  machines   are  constructed  so   that   the 

whole  current  traverses  the  coils  of  the  field  magnets, 
being  single  current  machines,  in  which  the  reaction 
principle  is  employed.  In  the  case  of  the  machine  desig- 
nated A2,  the  commutators  are  so  arranged  as  to  permit 
the  use  of  two  separate  circuits  when  desired. 

For  the  purpose  of  preserving  a  ready  measure  of  the 
current  produced  by  each  machine,  under  normal  con- 
ditions, a  shunt  was  constructed  by  which  an  inconsider- 
able but  definite  proportion  of  the  current  was  caused  to 
traverse  the  coils  of  a  galvanometer,  thus  giving  with 
each  machine  a  convenient  deflection,  which  could  at  any 


COMPARATIVE  EFFICIENCY  OF  VARIOUS  MACHINES.     61 

time  be  reproduced.  As  the  interposition  of  this  shunt  in 
the  circuit  did  not  appreciably  increase  its  resistance,  the 
normal  conditions  of  running  were  preserved. 

As  indicating  the  preservation  of  normal  conditions  in 
any  case,  the  speed  of  running  and  the  resistances  being 
the  same  as  in  any  previous  run,  it  was  found  that  when 
there  was  an  equal  expenditure  of  power,  as  indicated  by 
the  dynamometer,  the  current  produced,  as  indicated  by 
the  galvanometer,  was  in  each  case  the  same. 

Certain  of  the  machines  experimented  with  heated 
considerably  on  a  prolonged  run ;  most  of  the  tests,  there- 
fore, were  made  when  the  machines  were  as  nearly  as 
possible  at  about  the  temperature  of  the  surrounding 
air. 

It  is  evident  that  no  other  standard  could  be  well 
adopted,  as  under  a  prolonged  run  the  temperature  of  the 
different  parts  of  the  machine  would  increase  very  un- 
equally ;  and,  moreover,  it  would  be  impossible  to  make 
any  reliable  measurements  of  the  temperatures  of  many 
such  parts. 

In  measuring  the  resistance  of  the  machines,  a  Wheat- 
stone's  bridge,  with  a  sliding  contact,  was  used  in  con- 
nection with  a  galvanometer  and  a  suitable  voltaic  battery. 
In  taking  the  resistances  of  the  machines,  several  measure- 
ments were  made  with  the  armatures  in  different  positions, 
and  the  mean  of  these  measurements  taken  as  the  true 
resistance. 

To  determine  the  value  of  the  current,  two  methods 
were  selected,  one  based  on  the  production  of  heat  in  a 
circuit  of  known  resistance,  and  the  other  upon  the  com- 
parison of  a  definite  proportion  of  the  current  with  that 
of  a  Daniell's  battery. 

In  the  application  of  the  first  method,  eight  litres  of 
water,  at  a  known  temperature,  were  taken  and  placed  in 
a  suitable  non-conducting  vessel.  In  this  was  immersed 
a  German-silver  wire,  and  a  sliding  contact  adjusted  to 


62  ELECTRIC  TRANSMISSION  OF   POWER. 

afford  a  resistance  equal  to  that  of  the  exterior  resistance 
under  consideration. 

This  was  now  introduced  into  the  circuit  of  the  machine. 
All  these  arrangements  having  been  made,  the  temperature 
of  the  water  was  accurately  obtained  by  a  delicate  ther- 
mometer. The  current  from  the  machine  running  under 
normal  conditions  was  allowed  to  pass,  for  a  definite  time, 
through  the  calorimeter  so  provided.  From  the  data  thus 
obtained,  after  making  the  necessary  corrections  as  to  the 
weight  of  the  water  employed,  the  total  heating  effect  in 
the  exterior  circuit,  as  given  in  Table  II.,  was  deduced. 

Since  the  heat  in  various  portions  of  an  electrical 
circuit  is  directly  proportional  to  the  resistance  of  those 
portions,  the  total  heat  of  the  circuit  was  easily  calculated, 
and  is  given  in  Table  III.,  in  English  heat  units. 

For  ease  of  reference,  the  constant  has  been  given  for 
conversion  of  these  units  into  the  now  commonly  accepted 
units  of  heat. 

Having  thus  obtained  the  heating  effect,  the  electrical 
current  is — 


X  772 


where  C  =  the  weber  current  per  ohm  ;  "W,  the  weight  of 
water  in  pounds  ;  h,  the  increase  of  temperature  in  degrees 
Fahr.  ;  772,  Joule's  constant  ;  E,  the  resistance  in  ohms  ; 
t,  the  time  in  seconds;  and  c,  the  constant  0-737335,  the 
equivalent  in  foot-lbs.  of  one  weber  per  ohm  per  second. 
The  currents  so  deduced  for  the  different  machines  are 
given  in  Table  IV. 

The  other  method  employed  for  measuring  the  current, 
viz.  the  comparison  of  a  definite  portion  thereof  with  the 
current  from  a  Daniell's  battery,  was  as  follows  :  — 

A  shunt  was  constructed,  of  which  one  division  of  the 
circuit  was  0-12  ohm  and  the  other  3000  ohms.  In  this 
latter  division  of  the  circuit  was  placed  a  low-resistance 


COMPAEATIVE  EFFICIENCY  OF  VAEIOUS  MACHINES.     63 


galvanometer,  on  which  convenient  deflections  were 
obtained.  This  shunt  being  placed  in  the  circuit  of  the 
machine,  the  galvanometer  deflections  were  carefully 
noted.  These  substituted  resistances  were  immersed  in 
water,  in  order  to  maintain  an  equable  temperature. 

Three  Daniell's  cells  were  carefully  set  up  and  put  in 
circuit  with  the  same  galvanometer,  and  with  a  set  of 
standard  resistance  coils.  Eesistances  were  unplugged 
sufficient  to  produce  the  same  deflections  as  those  noted 
with  the  shunt  above  mentioned. 

The  shunt  ratio,  as  nearly  as  could  conveniently  be 
obtained,  was  g^-fonj-.  Then  the  formula 


c  = 


sn  xl'079? 

ir~ 


where  C  equals  the  weber  current ;  s,  the  reciprocal  of  the 
shunt  ratio ;  n,  the  number  of  cells  employed  ;  1-079,  the 
assumed  normal  value  of  the  electro- motive  force  of  a 
Daniell's  cell,  and  JR,  the  resistances  in  the  circuit  with 
the  battery,  gives  at  once  the  current.  In  comparison 
with  the  total  resistances  of  the  circuit,  the  internal 
resistance  of  the  battery  was  so  small  as  to  be  neglected. 
The  results  obtained  were  as  follows : — 


Name  of  Machine. 

Shunt 
Ratio. 

Number  of 
Daniell's 
Cells. 

Resistances 
Unplugged 

Speed 
of 

Machine. 

3 

Ohms. 
2  710 

Revo- 
lutions. 
1  340- 

Small  Brush      

3  700 

1  400 

Wallace-Farmer     .      .      .     .1 
Gramme      .           .     . 

j  > 
»  > 

»  » 
i  > 

8,320 
6,980 
4  800 

844 
1,040 
800 

>  » 

•>  i 

The  weber  currents,  as  calculated  from  the  above  data, 
are  given  in  Table  IV. 


64 


ELECTRIC   TRANSMISSION  OF  POWER. 


From  the  results  thus  derived,  the  electro-motive  force 
was  deduced  by  the  general  formula, 

E  =  C  x  R. 

The  electro-motive  force  thus  calculated  will  be  found 
in  Table  IV. 

TABLE  L* — SHOWING  WEIGHT,  POWER  ABSORBED,  &c.,  BY  DYNAMO- 
ELECTRIC  MACHINES,  TESTED  BY  A  COMMITTEE  OF  THE  FRANKLIN 
INSTITUTE,  1877-78. 


A                  Copper-  wire  in  — 

£ 

00    .- 

Name  of 
Machine. 

c 
^          Armature. 

Field  Magnets. 

•25* 

ts  || 

pounds  of 
Power 

HP. 

•§3 

ila 

£        Size. 

Weight. 

Size. 

Weight. 

s 

Inch. 

Ibs. 

Inch. 

Ibs. 

Large  Brush 

475   0-081 

32 

0-134 

100 

1,340 

107-606 

3-26 

Small     „ 

390   0-063 

24 

0-096 

80 

1,400 

124-248 

3-76 

Large  Wal-j 

600   0-042 

50 

0-114 

125 

800 

' 

lace  .      ./ 

Small     „ 

350   0-043 

18f 

0-098 

41 

1,000 

128-544 

3-89 

Gramme    . 

366   0-059 

104 

0-108 

104 

800 

60-992 

1-84 

Statements  are  frequently  made,  when  speaking  of 
certain  dynamo-electric  machines,  that  they  are  equal  to 
a  given  number  of  Darnell's  or  other  well-known  battery 
cells.  It  is  evident,  however,  that  no  such  comparison 
can  properly  be  made,  since  the  electro-motive  force  of  a 
dynamo-electric  machine,  in  which  the  reaction  principle 
is  employed,  changes  considerably  with  any  change  in  the 
relative  resistances  of  the  circuit  of  which  it  forms  a  part, 
while  that  of  any  good  form  of  battery,  disregarding  pola- 
risation, remains  approximately  constant.  The  internal 


*  These  reports  have  been  condensed  to  show  merely  the  power  ex- 
pended and  returnable  by  dynamo-electric  machines. 


COMPARATIVE  EFFICIENCY  OF  VARIOUS  MACHINES.     65 

resistance  of  dynamo-electric  machines  is,  as  a  rule,  very 
much  lower  than  that  of  any  ordinary  series  of  battery 
cells,  as  generally  constructed,  and  therefore,  to  obtain 
with  a  battery  conditions  equivalent  to  those  in  a  dynamo- 
electric  machine,  a  sufficient  number  of  cells  in  series  would 
have  to  be  employed  to  give  the  same  electro-motive  force  ; 
while,  at  the  same  time,  the  size  of  the  cells,  or  their 
number  in  multiple  arc,  would  require  to  be  such  that  the 
internal  resistance  should  equal  that  of  the  machine. 

Suppose,  for  example,  that  it  be  desired  to  replace  the 
large  Brush  machine  by  a  battery  whose  electro -motive 
force  and  internal  and  external  resistances  are  all  equal 
to  that  of  the  machine,  and  that  we  adopt  as  a  standard 
a  Daniell's  cell,  of  an  internal  resistance  of,  say,  one  ohm. 
Eeferring  to  Table  IV.,  the  electro- motive  force  of  this 
machine  is  about  39  volts,  to  produce  which  about 
37  cells,  in  series,  would  be  required ;  but,  by  Table  II., 
the  internal  resistance  of  this  machine  is  about  0  •  49  ohm. 
To  reduce  the  resistance  of  our  standard  cells  to  this 
figure,  when  37  cells  are  employed  in  series,  76  cells  in 
multiple  arc  would  be  required.  Therefore,  the  total 
number  of  cells  necessary  to  replace  this  machine  would 
equal  37  X  76,  or  2812  cells,  working  over  the  same 
external  resistance.  It  must  be  borne  in  mind,  however, 
that  although  the  machine  is  equal  to  2812  of  the  cells 
taken,  that  no  other  arrangement  of  these  cells  than  that 
mentioned,  viz.  76  in  multiple  arc  and  37  in  series,  could 
reproduce  the  same  conditions,  and,  moreover,  the  external 
resistances  must  be  the  same.  The  same  principles 
applied  to  other  machines  would,  when  the  internal 
resistance  was  great,  require  a  large  number  of  cells,  but 
arranged  in  such  a  way  as  to  be  extremely  wasteful,  from 
by  far  the  greater  portion  of  the  work  being  done  in  over- 
coming the  resistance  of  the  battery  itself. 

The  true  comparative  measure  of  the  efficiency  of 
dynamo-electric  machines  as  means  for  converting  motive- 


66  ELECTRIC  TRANSMISSION   OF  POWER. 

power  into  work  derived  from  electrical  currents,  is  found 
by  comparing  the  units  of  work  consumed  with  the  equi- 
valent unit  of  work  appearing  in  the  circuit  external  to  the 
machine.  In  Table  V.  the  comparative  data  are  given. 

The  heat  due  to  local  circuits  in  the  conducting  masses 
of  metal  in  the  machines,  irrespective  of  the  wire,  consumes 
force  in  what  may  be  conveniently  described  as  the  local 
action  of  the  machine,  and  is  manifestly  comparable  to  the 
well-known  local  action  of  the  voltaic  battery,  since  in 
each  case  it  not  only  acts  to  diminish  the  effective  current 
produced  but  also  adds  to  the  cost. 

No  determinations  made  with  an  unknown  or  abnormal 
external  resistance  can  be  of  any  value,  since  the  propor- 
tion of  work  done,  in  the  several  portions  of  an  electrical 
circuit,  depends  upon  and  varies  with  the  resistances  they 
offer  to  its  passage.  If,  therefore,  in  separate  determina- 
tions with  any  particular  machine,  the  resistance  of  that 
part  of  a  circuit  the  work  of  which  is  measured,  be  in  one 
instance  large  in  proportion  to  the  remainder  of  the 
circuit,  and  in  another  small,  the  two  measurements  thus 
made  would  give  widely  different  results,  since  in  the 
case  where  a  large  resistance  was  interposed  in  this  part 
of  the  circuit,  the  percentage  of  the  total  work  appearing 
there  would  be  greater  than  if  the  small  resistance  had 
been  used.  Wherever  an  attempt  has  been  made  to  deter- 
mine the  efficiency  of  a  single  machine,  or  of  the  relative 
efficiency  of  a  number  of  machines,  by  noting  the  quantity 
of  gas  evolved  in  a  voltameter,  or  by  the  electrolysis  of 
copper  sulphate  in  a  decomposing  cell,  when  the  resist- 
ance of  the  voltameter  or  decomposing  cell  did  not 
represent  the  normal  working  resistance,  it  is  manifest 
that  the  results  cannot  properly  be  taken  as  a  measure  of 
the  actual  efficiency. 

During  any  continued  run,  the  heating  of  the  wire  of 
the  machine,  either  directly  by  the  current,  or  indirectly 
from  conduction  from  those  parts  of  the  machine  heated 


COMPAEATIVE  EFFICIENCY  OF  VAKIOUS  MACHINES.     67 

by  local  action,  as  explained  in  a  former  part  of  this 
report,  produces  an  increased  resistance,  and  a  consequent 
falling  off  in  the  effective  current.  Thus,  in  Table  II.,  at 
the  temperature  of  73-5°  Fahr.,  A1,  the  large  Brush 
machine,  had  a  resistance  of  0  •  485  ohms,  while  at  88°  Fahr., 
at  the  armature  coils,  it  was  0*495  ohm.  These  differences 
were  still  more  marked  in  the  case  of  B1. 

In  A2,  the  small  Brush  machine,  it  will  be  noticed  that 
two  separate  values  are  given  for  the  resistance  of  the 
machine.  These  correspond  to  different  connections,  viz. 
the  resistance,  1*239  ohms,  being  the  connection  at  the 
commutator  for  low  resistance,  the  double  conducting 
wires  being  coupled  in  multiple  arc,  while  5*044  ohms 
represent  the  resistance  when  the  sections  of  the  double 
conductor  are  coupled  at  the  commutator  in  series. 

Eeferring  to  Table  III.,  the  numbers  given  in  the 
column  headed  "  Heat  in  external  circuit "  are  the  measure 
of  the  total  heating  power  in  that  portion  of  the  circuit 
external  to  the  machine. 

In  the  column  headed  "  Total  heat  of  circuit "  are 
given  the  quantities  of  heat  developed  in  the  whole 
circuit,  which  numbers,  compared  with  those  in  the  pre- 
ceding column,  furnish  us  with  the  relative  proportions  of 
the  work  of  the  circuit,  which  appear  in  the  external 
circuit. 

The  column  headed  "  Heat  per  ohm  per  second  "  gives 
the  relative  work  per  ohm  of  resistance  in  each  case,  and 
these  numbers,  multiplied  by  the  total  resistance,  give  the 
total  energy  of  the  current  expressed  in  heat  units  per 
second. 

In  Table  IV.  are  given  the  results  of  calculation  and 
measurement  as  to  the  electrical  work  of  each  machine. 

It  is  evident  to  those  acquainted  with  the  principles  of 
electrical  science,  that  in  the  weber  current  and  the  unit 
electro-motive  force,  we  have  the  data  for  comparing  the 
work  of  these  machines  with  that  of  any  other  machine  or 

F  2 


68 


ELECTRIC  TRANSMISSION  OF  POWER. 


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COMPARATIVE  EFFICIENCY  OF  VARIOUS  MACHINES.     69 


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ELECTEIC   TRANSMISSION   OF   POWER. 


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COMPARATIVE  EFFICIENCY  OF  VARIOUS  MACHINES.     71 

battery,  whether  used  for  light,  heat,  or  electrolysis,  or 
any  other  form  of  electrical  work. 

The  values  of  the  weber  current,  as  deduced  from  the 
heat  developed,  and  from  the  comparison  with  a  Daniell's 
cell,  do  not  exactly  agree;  nor  could  this  have  been 
expected,  when  the  difficulty  of  minutely  reproducing  the 
conditions  as  to  speed,  resistance,  etc.,  is  considered. 

By  comparison  of  the  electro-motive  force  of  the  different 
machines,  it  appears  that  no  definite  unit  seems  to  have 
been  aimed  at  by  all  the  makers. 

Table  Y.  is  designed  especially  to  permit  a  legitimate 
comparison  of  the  relative  efficiency  in  converting  motive- 
power  into  current.  The  actual  dynamometer  reading  is 
given  in  the  first  column.  On  account  of  the  differences 
of  construction  and  differences  in  speed  of  running,  the 
friction  and  resistance  of  the  air  vary  greatly,  being  least 
with  the  Gramme,  as  might  be  expected,  since  the  form 
of  the  revolving  armature  and  the  speed  of  the  machine 
conduce  to  this  result.  This  is,  of  course,  a  point  greatly 
in  favour  of  the  Gramme  machine. 

That  portion  of  the  power  expended  available  for  pro- 
ducing current  is  given  in  the  third  column,  being  the 
remainder,  after  deducting  the  friction,  as  above  men- 
tioned ;  but  this  power  is  not  in  any  case  fully  utilised  in 
the  normal  circuit.  This  is  found  to  be  the  case  by  com- 
paring calculations  of  the  total  work  of  the  circuit  in 
foot-lbs.  expended  in  producing  such  current  as  given  in 
the  appropriate  column. 

For  instance,  in  the  case  of  A1,  the  large  Brush  machine, 
the  available  force  for  producing  current  is  89,656  foot-lbs. 
per  minute,  of  which  only  53,646  reappear  as  heat  in  the 
circuit.  The  balance  is  most  probably  expended  in  the 
production  of  local  currents  in  the  various  conducting 
masses  of  metal  composing  the  machine.  The  amount 
thus  expended  in  local  action  is  given  in  the  column 
designated  "F.  P.,  unaccounted  for  in  the  circuit."  A 


72 


ELECTRIC   TRANSMISSION   OF  POWER. 


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COMPARATIVE  EFFICIENCY  OF  VARIOUS  MACHINES.     73 

comparison  of  the  figures  in  this  column  is  decidedly  in 
favour  of  the  Gramme  machine,  it  requiring  the  smallest 
proportion  of  power  expended  to  be  lost  in  local  action. 
When,  however,  we  consider  that  the  current  produced 
by  the  large  Brush  machine  is  nearly  double  that  pro- 
duced by  the  Gramme,  the  disproportion  in  the  local 
action  is  not  so  great. 

The  determinations  made  enabled  the  following  opinions 
to  be  formed  as  to  the  comparative  merits  of  the  machines 
submitted  for  examination  : — 

The  Gramme  machine  is  the  most  economical,  con- 
sidered as  a  means  for  converting  motive-power  into 
electrical  current,  giving  a  useful  result  equal  to  38  per 
cent.,  or  to  41  per  cent.,  after  deducting  friction  and 
the  resistance  of  the  air.  In  this  machine  the  loss  of 
power  in  friction  and  local  action  is  the  least,  the  speed 
being  comparatively  low. 

The  large  Brush  machine  comes  next  in  order  of  effi- 
ciency, giving  useful  effect  equal  to  31  per  cent,  of  the 
total  power  used,  or  37^  per  cent,  after  deducting  friction. 
This  machine  is,  indeed,  but  little  inferior  in  this  respect 
to  the  Gramme,  having,  however,  the  disadvantage  of 
high  speed,  and  a  greater  proportionate  loss  of  power  in 
friction,  etc.  This  loss  is  nearly  compensated  by  the 
advantage  this  machine  possesses  over  the  others  of  working 
with  a  high  external,  compared  with  the  internal,  resist- 
ance, this  also  insuring  comparative  absence  of  heating  in 
the  machine.  This  machine  gave  the  most  powerful 
current. 

The  small  Brush  machine  stands  third  in  efficiency, 
giving  a  useful  result  equal  to  27  per  cent.,  or  31  per 
cent,  after  deducting  friction.  Although  somewhat 
inferior  to  the  Gramme,  it  is,  nevertheless,  a  machine 
admirably  adapted  to  the  production  of  intense  currents, 
and  has  the  advantage  of  being  made  to  furnish  currents 
of  widely  varying  electro-motive  force.  By  suitably 


74  ELECTEIC  TRANSMISSION  OF  POWER. 

connecting  the  machine,  as  before  described,  the  electro- 
motive force  may  be  increased  to  over  120  volts.  It 
possesses,  moreover,  the  advantage  of  division  of  the 
conductor  into  two  circuits,  a  feature  which,  however,  is 
also  possessed  by  some  forms  of  other  machines.  The 
simplicity  and  ease  of  repair  of  the  commutator  are  also 
advantages.  Again,  this  machine  does  not  heat  greatly. 

The  Wallace-Farmer  machine  does  not  return  to  the 
effective  circuit  as  large  a  proportion  of  power  as  the 
other  machines,  although  it  uses,  in  electrical  work,  a 
large  amount  of  power  in  a  small  space.  The  cause  of  its 
small  economy  is  the  expenditure  of  a  large  proportion  of 
the  power  in  the  production  of  local  action.  By  remedying 
this  defect  a  very  admirable  machine  would  be  produced. 
After  careful  consideration  of  all  the  facts,  the  Committee 
unanimously  concluded  that  the  small  Brush  machine, 
though  somewhat  less  economical  than  the  Gramme  ma- 
chine, or  the  large  Brush  machine,  was,  of  the  machines 
experimented  with,  the  best  adapted  for  the  various  pur- 
poses of  the  Institute,  chiefly  for  the  following  reasons: 
It  is  adapted  to  the  production  of  currents  of  widely- 
varying  electro-motive  force,  and  from  the  mechanical 
details  of  its  construction,  especially  at  the  commutators, 
it  possesses  great  ease  of  repair  to  the  parts  subject  to 
wear. 

During  the  competitive  trials  at  the  Franklin  Institute, 
as  to  the  relative  efficiency  of  the  machines,  as  noted  in 
the  preceding  pages,  Professors  Houston  and  Thomson 
took  the  opportunity  thus  afforded  to  make  a  careful 
study  of  many  interesting  circumstances  which  influence 
the  efficiency  of  these  machines. 

A  convenient  arrangement  of  the  particular  circum- 
stances to  be  discussed  is :  (1)  those  affecting  the  internal 
work  of  the  machines ;  (2)  those  affecting  the  external 
work;  and  (3)  the  relations  between  the  internal  and 
external  work. 


COMPARATIVE  EFFICIENCY  OF  VARIOUS  MACHINES.    75 

The  mechanical  energy  employed  to  give  motion  to  a 
dynamo-electric  machine  is  expended  in  two  ways  :  (1) 
in  overcoming  the  friction  and  the  resistance  of  the  air ; 
and  (2)  in  moving  the  armature  of  the  machine  through 
the  magnetic  field,  the  latter,  of  course,  constituting  solely 
the  energy  available  for  producing  electrical  currents. 
The  greatest  amount  of  power  expended  in  the  first  way 
was  noticed  to  be  about  17  per  cent,  of  the  total  power 
employed.  This  expenditure  was  clearly  traceable  to  the 
high  speed  required  by  the  machine.  The  speed,  there- 
fore, required  to  properly  operate  a  machine  is  an  import- 
ant factor  in  ascertaining  its  efficiency.  The  above  percent- 
age of  loss  may  not  appear  great ;  but  when  it  is  com- 
pared with  the  total  work  done  in  the  external  circuit, 
constituting  as  it  did  in  this  particular  instance  over 
50  per  cent,  of  the  latter,  and  about  33  per  cent,  of  the 
total  work  of  the  circuit,  its  influence  is  not  to  be  dis- 
regarded. In  another  instance  the  work  consumed  as 
friction  was  equal  to  about  80  per  cent,  of  that  appearing 
in  the  external  circuit  as  heat,  while  in  the  Gramme 
machine  experimented  with  this  percentage  fell  to  20,  and 
was  only  about  7  per  cent,  of  the  total  power  consumed  in 
driving  the  machine. 

In  regard  to  the  second  way  in  which  mechanical 
energy  is  consumed,  in  overcoming  the  resistance  neces- 
sary to  move  the  armature  through  the  magnetic  field,  or, 
in  other  words,  to  produce  electrical  currents,  it  must  not 
be  supposed  that  all  this  electrical  work  appears  in  the 
circuit  of  the  machine,  since  a  considerable  portion  is 
expended  in  producing  local  circuits  in  the  conducting 
masses  of  metal,  other  than  the  wire,  composing  the 
machine. 

The  following  instances  of  the  relation  between  the 
actual  work  of  the  circuit,  and  that  expended  in  local 
action,  will  show  that  this  latter  is  in  no  wise  to  be 
neglected.  In  one  instance  an  amount  of  power,  some- 


76  ELECTEIC  TRANSMISSION  OP  POWER. 

what  more  than  double  the  total  work  of  the  circuit,  was 
thus  expended.  In  another  instance  it  constituted  less 
than  one-third  the  total  work  of  the  circuit. 

Of  course,  work  expended  in  local  action  is  simply 
thrown  away,  since  it  adds  only  to  the  heating  of  the 
machine.  And,  since  the  latter  increases  its  electrical 
resistance,  it  is  doubly  injurious. 

The  local  action  of  dynamo-electric  machines  is  analo- 
gous to  the  local  action  of  a  battery,  and  is  equally 
injurious  in  its  effect  upon  the  available  current. 

Again,  in  regard  to  the  internal  work  of  a  machine, 
since  all  this  is  eventually  reduced  to  heat  in  the  machine, 
the  temperature  during  running  must  continually  rise 
until  the  loss  by  radiation  and  convection  into  the  sur- 
rounding air  equals  the  production,  and  thus  the  machine 
will  acquire  a  constant  temperature.  This  temperature, 
however,  will  differ  in  different  machines,  according  to 
their  construction,  and  to  the  power  expended  in  pro- 
ducing the  internal  work,  being,  of  course,  higher  when 
the  power  expended  in  producing  the  internal  work  is 
proportionally  high. 

If,  therefore,  a  machine  during  running  acquires  a  high 
temperature  when  a  proper  external  resistance  is  employed, 
its  efficiency  will  be  low.  But  it  should  not  be  supposed 
that  because  a  machine,  when  run  without  external  re- 
sistance— that  is,  on  short  circuit — heats  rapidly,  that 
inefficiency  is  shown  thereby.  On  the  contrary,  should  a 
machine  remain  comparatively  cool  when  a  proper  ex- 
ternal resistance  is  employed,  and  heat  greatly  when  put 
on  short  circuit,  these  conditions  should  be  regarded  as  a 
proof  of  its  efficiency. 

In  regard  to  the  second  division,  the  external  work  of 
the  machine,  this  may  be  applied  in  the  production  of 
light,  heat,  electrolysis,  magnetism,  &c. 

Perhaps  the  highest  estimate  that  can  be  given  of  the 
efficiency  of  dynamo-electric  machines,  as  ordinarily  used, 


COMPAKATIVE  EFFICIENCY  OF  VARIOUS  MACHINES.     77 

is  not  over  50  per  cent.;  measurements  have  not  given 
more  than  38  per  cent.  Future  improvements  may  in- 
crease this  proportion.  Since  the  efficiency  of  an  ordinary 
steam-engine  and  boiler  in  utilising  the  heat  of  the  fuel 
is  probably  over-estimated  at  20  per  cent.,  the  apparent 
maximum  percentage  of  heat  that  could  be  recovered  from 
the  current  developed  in  a  dynamo-electric  machine 
would  be  over-estimated  at  10  per  cent.  The  economical 
heating  of  buildings  by  means  of  electricity  may,  there- 
fore, be  regarded  as  totally  impracticable. 

In  respect  to  the  relations  that  should  exist  between 
the  external  and  the  internal  work  of  dynamo-electric 
machines,  it  will  be  found  that  the  greatest  efficiency  will, 
of  course,  exist  where  the  external  work  is  much  greater 
than  the  internal  work,  and  this  will  be  proportionally 
greater  as  the  external  resistance  is  greater. 


78  ELECTRIC  TRANSMISSION  OF  POWER. 


CHAPTER  IX. 

OTHER   THEORETICAL   CONSIDERATIONS. 

MR.  DESMOND  FITZGERALD  lias  pointed  out  that  in  the  case 

•pi 

of  any  electro-motor  the  equation  I  =  —  is  strictly  ap- 
plicable. 

In  the  voltaic  battery,  however,  a  variation  of  E  does 
not  necessarily  affect  E  which  is  altogether  independent 
of  such  variation  when  this  occurs  in  the  external  portion 

of  the  circuit.     Thus  we  have  generally  I  cc  — ,  or  current 

varies  inversely  as  the  resistance  in  circuit. 

Again,  a  variation  of  E  does  not  necessarily  affect  R  ; 
and,  when  the  external  resistance  of  the  circuit  bears  a 
high  ratio  to  the  battery  resistance,  a  variation  of  the 
electro-motive  force,  from  E  to  Ex — and  addition  to,  or 
diminution  of,  the  number  of  cells  in  series — causes  the 

TT 
current  to  vary  approximately  in  the  ratio  =*   Accurately, 

the   variation   in   any  case   is   determined   by  the   ratio 

TT    T? 

^      *  — — »  when  p  is  the  resistance  of  the  cell  or  cells 
&  K  -f-  ±jj  p 

added  or  subtracted.     Thus, 

E1  Ex  R  E! 

E    X  ER-j-Ep  ~  R+7 

Thus,  in  the  case  of  a  telegraph  circuit,  for  instance,  we 
have,  approximately,  I  cc  E.     On  the  other  hand,  in  the 


OTHER  THEORETICAL  CONSIDERATIONS.  79 

dynamo-electric  machine,  converting  into  electrical  work 

1  E2 

a  given  HP.,  I  cc  —  =.,  since  the  ratio  —  being  constant, 
f    K  -ti 


E2  cc  K,  E  x  /X  and       cc  --~  =  --L.      Thus,   any 


variation  of  B  in  this  case  necessarily  affects  E. 

Again,  any  variation  of  E  necessarily  affects  R  ;  and  the 

product  E  I  being  constant,  we  have  I  x  =,  a  somewhat 

Jij 

startling  result,  which  to  some  observers  has  appeared 
contradictory  to  the  law  of  Ohm.  With  this,  however,  it 
is  in  perfect  accord  —  in  effect,  since  E  cc  J  K,  R  cc  E2, 

E       E        1 

and  —  x  —  =  -  ;  or,  when  E  is  varied,  the  current  varies 
xv        xj-1        jit 

inversely  as  the  electro-motive  force,  because  the  resistance 
varies  as  the  square  of  this  value. 

It  will  be  seen  that  R  cc  E2  -  —  ,  and  that  the  same 

quantity  of  work  will  be  done  by  the  current  whatever 
may  be  the  resistance  in  circuit. 

If  hp.  be  taken  to  express  the  total  horse-power  con- 
verted into  electrical  work  (in  the  whole  circuit),  under 
the  best  conditions,  with  a  Gramme  machine  of  the  form 
experimented  with  at  the  Franklin  Institute, 

HP.  =  hp.  X  1-39, 

and  the  efficiency  of  the  machine  is  expressed  by 
hp. 


HP. 


=  0-72  (nearly). 


Or  the  machine  can  convert  into  electrical  work  72  per 
cent,  of  the  energy  expended  upon  it. 

The  ratio  •=—  is  the  measure  of  the  efficiency  of  dynamo- 


80  ELECTRIC  TRANSMISSION  OF  POWER. 

electric  machines.     In  the  case  of  the  Gramme  machine 
under  the  best  conditions,  we  have 

HP.  =  hp.  x  1-39. 

Mr.  L.  Schwendler  has  observed  that  the  currents  pro- 
duced by  dynamo-electric  machines,  as  the  insertion  of  a 
Bell  telephone  (used  as  a  shunt)  will  easily  prove,  are  not 
steady.  The  dynamo-electric  machine  with  the  greatest 
number  of  sections  in  the  induction  cylinder  gives  the 
steadiest  current.  Twelve  sections  are  found  to  be  neces- 
sary and  sufficient.  That  the  current  produced  by  any 
dynamo-electric  machine  through  a  given  constant  total 
resistance  in  circuit  increases  permanently  with  the  speed 
of  the  induction  cylinder.  This  increase  of  current  for 
low  speeds  is  more  than  proportional  to  the  speed ;  after- 
wards it  becomes  proportional,  and  for  high  speeds  the 
increase  of  current  is  less  than  proportional  to  the  speed. 
The  current  has,  however,  no  maximum  for  any  speed,  but 
reaches  its  greatest  value  at  an  infinite  speed.  This  same 
law,  as  the  total  resistance  in  circuit  is  supposed  to  be 
constant,  of  course  holds  good  also  for  the  electro-motive 
force  of  the  dynamo-electric  machine. 

Keeping  the  speed  constant,  the  electro-motive  force  of 
any  dynamo-electric  machine  decreases  rapidly  with  in- 
crease of  external  resistance.  This  decrease  is  more  rapid 
the  smaller  the  internal  resistance  of  the  dynamo-electric 
machine  is  made.  Hence  the  currents  must  decrease  much 
more  rapidly  than  proportional  to  the  total  resistance  in 
circuit.  As  in  the  case  of  speed,  the  electro-motive  force 
has  no  maximum  for  a  certain  external  resistance,  but 
approaches  permanently  its  greatest  value  for  an  external 
resistance  equal  nil.  It  appears  that  the  function  which 
connects  electro-motive  force  and  speed  is  the  same  as 
that  which  connects  electro-motive  force  and  external 
resistance.  We  have  only  to  substitute  for  speed  the 


OTHER   THEOKETICAL   CONSIDERATIONS.  81 

inverse  of  resistance,  and  vice  versa.  As  to  the  maximum 
work  by  a  current  in  a  resistance  r,  the  current  decreased 
much  more  rapidly  than  the  total  resistance  in  circuit 
increased,  and  this  resistance  r  should  invariably  be  made 
smaller  than  the  remaining  resistance  of  the  circuit,  i.e., 
smaller  than  the  internal  resistance  of  dynamo-electric 
machines  plus  resistance  of  leading  wires. 

With  regard  to  the  electro-motive  force  of  a  dynamo- 
electric  machine  as  a  function  of  the  resistance  and  speed, 
it  appears  that  the  formulae  are  most  probably  correct  for 
all  dynamo-electric  machines  if  the  loss  of  current  by 
transmission  is  taken  into  account : 


E  being  the  E  M  F,  ra  the  internal  resistance,  and  r  the  ex- 
ternal resistance,  including  resistance  of  leading  wire. 
k  and  a  are  independent  of  m  and  r,  and  are  the  functions 
of  the  speed  of  the  induction  cylinder,  containing  also  the 
construction  coefficients,  e  is  the  basis  of  the  natural 
logarithm.  Further, 


E1  =  K 


E1  being  the  E  M  F,  and  v  the  speed  of  the  induction 
cylinder.  kl  and  a1  are  independent  of  v  and  are  functions 
of  m  and  r  only.  These  two  functions,  E  and  E1,  correspond 
to  all  the  characteristics  of  the  curves  found  by  experi- 
ment, and  they  also  fulfil  the  limit  conditions. 

In  respect  to  the  regularity  of  the  production  of  currents 
by  dynamo-electric  machines  at  different  periods,  if  the 
brushes  are  well  set,  and  if  they  are  placed  as  nearly  as 

G 


82  ELECTRIC   TRANSMISSION  OF   POWER. 

possible  in  the  neutral  line  of  the  commutator,*  the  pro- 
.duction  of  current  is  perfectly  regular,  and  measurements 
taken  through  the  same  external  resistance  at  the  most 
distant  periods  agree  most  perfectly  with  each  other,  sup- 
posing the  correction  for  variation  in  speed  and  internal 
resistance  to  be  applied.  Disregarding  the  heating  of  the 
dynamo-electric  machine  by  the  current,  the  time  required 
to  arrive  at  dynamic  equlibrium,  i.e.,  when  force  trans- 
mitted, current,  and  magnetism  received  are  constant,  is 
very  short  indeed,  especially  for  strong  currents. 

As  the  power  which  is  represented  by  the  measured 
current  working  through  a  given  resistance  can  never 
exceed  the  original  power  transmitted  to  the  machine,  we 
can,  from  current,  resistance,  and  force  measurements, 
frame  a  formula  which  checks  the  probability  of  the 
results.  This  formula  is  : 


C<0.33^/^^. 
r-\~m 

W1  is  the  total  power  consumed  by  any  dynamo-electric 
machine  when  producing  the  observed  current  C  in  a 
circuit  of  resistance  r  -j-  m ;  wl  is  the  power  consumed  by 
the  dynamo-electric  machine  when  producing  no  current 
(i.e.  driven  empty,  circuit  open,  external  resistance  in- 
finite) ;  r  is  the  external  resistance,  and  m  the  internal 
resistance.  In  the  above  formula  C  is  in  webers,  W1  and 
wl  in  meg-ergs  per  second,  and  r  and  m  in  Siemens' 
units.  Of  late,  exaggerated  statements  of  the  performance 
of  dynamo-electric  machines  have  been  made,  the  absurdity 
of  which  would  have  become  evident  at  once  if  the  above 
formula  had  been  applied  as  a  check  to  the  results. 

If  all  the  work  ( W1  —  wl)  were  transformed  into  available 


*  M.  A.  Breguet  states  that  the  maximum  and  steadiest  current 
results  from  the  brushes  being  placed  at  an  angle  with  the  neutral 
line,  dependent  in  amount  upon  v. 


OTHER   THEORETICAL   CONSIDERATIONS. 


83 


W1  —  10 
current  in  the  external  circuit,  then  —  —  —  =  unity,  where 

W  is  the  total  work  performed  by  the  observed  current  in 
a  circuit  of  known  resistance.     In  practice  it  will  be  found, 


. 
however,  that  --  >  1  (for  many  reasons).    This  ex- 


presson, 


,  is  called  the  coefficient  of  transmission, 


and  designated  by  the  letter  k.  k  is  different  for  the 
different  dynamo-electric  machines  which  have  been  tried, 
and  decreases  with  increase  of  current.  Producing  cur- 
rents above  24  webers,  the  following  average  vahies  of 
k  have  been  obtained  :  — 


i      Average  Current 
in  Webers. 

1 

•01 

31 

•0 

1 

•12 

31 

•1 

1 

•28 

27 

•9 

W 


,    w  is  the    useful  work  done   in  the   circuit 
W1  —  w1 

by  the  current  As  the  resistance  of  dynamo-electric 
machines  and  leading  wires  cannot  be  made  nil,  the 
coefficient  of  efficiency  must  be  always  smaller  than 
unity.  For  currents  above  24  webers,  we  have : — 


e.                  '      Average  Current. 

0-62 

29-5 

0-53 

31-0 

0-47 

32-6 

0-30 

27-9 

84  ELECTRIC  TRANSMISSION  OF   POWER. 

As  to  the  practical  mechanical  equivalent  of  the  currents 

W1  —  «?i 

produced  by  dynamo-electric  machines,  it  = ~ —  ,  where 

O 

0  is  the  current  in  webers.     Above  24  webers,  different 
dynamo-electric  machines  produce  the  weber  at  the  fol- 
lowing comsumption  of  power:  1   weber  at  686*5  meg- 
ergs  per  second,    1  weber   at  736  meg-ergs  per  second, 

1  weber  at  920  meg- ergs  per  second. 


CONCLUSIONS.  85 


CHAPTER  X. 

CONCLUSIONS. 

THE  feasibility  of  electric  transmission  of  power  having 
been  proved  from  consideration  of  mechanical  efficiency 
both  as  regards  current  developed  from  mechanical  power 
and  as  mechanical  power  reclaimed  from  the  current  thus 
produced,  we  have  learnt  from  unimpeachable  evidence 
that  the  power  reclaimed  may  easily  amount  to  48  per 
cent,  of  that  expended  in  the  first  instance.  This  amount 
of  reclaimed  power  is  indubitably  superior  to  that  obtained 
with  compressed  air,  and  approaches  the  practical  effi- 
ciency of  hydraulic  transmission.  Electric  transmission 
has,  however,  the  unparalleled  advantage  of  being  superior 
to  the  obstacle  presented  by  distance,  whilst  it  is  at  the 
same  time  easily  portable,  and  can  be  changed  in  direction, 
as  well  as  in  intensity,  at  will.  No  force  appears  in  the 
connecting  portions  or  conductor,  such  as  appears  during 
mechanical  transmission  with  shafting,  or  in  pipes  with 
compressed  air  or  water.  The  conductor  appears  inert, 
and  can  be  shifted,  bent,  or  in  any  way  moved  whilst 
transmitting  many  horse-power.  Its  continuity  must  not, 
of  course,  be  interrupted. 

The  source  of  power  and  the  point  of  reclamation  may 
be  relatively  situated  most  awkwardly,  but  the  electric 
conductor  can  be  brought  round  the  sharpest  corner,  or 
carried  through  the  most  private  room  without  incon- 
venience. There  is  nothing  to  burst  or  give  way.  The 
same  circuit  as  may  be  tapped  to  provide  the  means  of 
working  power-machinery  can  be  as  conveniently  tapped 
to  work  a  sewing-machine. 


86  ELECTRIC   TRANSMISSION   OF   POWER. 

In  mining  operations  electric  transmission  will  doubt- 
less become  of  the  highest  value,  since  it  involves  no 
danger.  Machines  for  this  purpose  could  be  easily  con- 
structed without  a  commutator,  so  that  sparks  could  be 
avoided,  with  only  small  loss  of  power.  The  ready 
portability  offers  great  inducements  to  the  mining 
engineer.  For  ploughing  by  power,  trials  made  in  France 
show  that  electricity  can  replace  steam  with  advantage 
and  economy.  And,  in  Scotland,  power  obtained  from  a 
waterfall  has  been  transmitted  one  mile  and  a  half. 

Dredges  could  be  reduced  in  size,  and  worked  from  a 
central  motor,  so  that  smaller  channels  could  be  cleansed 
mechanically  than  are  now  subject  to  this  method.  In 
mills  and  factories  inaccessible  rooms  can  be  utilised  for 
power- worked  machinery.  These  are  but  a  few  advan- 
tages. A  millennium  might  be  anticipated  when  the  water- 
power  of  a  country  shall  be  available  at  every  door,  for 
electric-power  conductors  can  be  laid  in  the  streets  more 
easily  than  gas  or  water-pipes. 

But,  says  the  economist,  what  about  cost?  Acknow- 
ledging these  great  advantages,  what  is  there  to  pay  for 
them  ?  And  the  economist  can  be  satisfactorily  answered. 
Leaving  out  of  count  the  scheme  proposed  by  Sir  William 
Thomson,  in  which  we  might  have  our  water  conveyed  to 
us  through  pipes,  the  metal  of  which  conducted  the 
electricity  for  our  power,  we  have  to  consider  what  is 
necessary  in  transmitting  power  electrically. 

First,  we  require  to  generate  our  electricity,  and  water- 
power  is,  of  course,  preferable  if  available.  If  not  avail- 
able to  generate  electricity,  it  surely  will  not  be  available 
to  compress  air  or  force  water,  because  these  are  only  to 
be  carried  through  comparatively  short  distances,  and  the 
original  power  question  may  be  cancelled  from  the  equation 
as  being  a  common  element.  Keference,  it  need  scarcely 
be  said,  is  made  only  to  cases  where  distance  is  involved. 
As  our  efficiency  is  good,  we  have  only  to  consider  (1)  the 


CONCLL'SibivS/ 


'••••••  87 


cost  of  the  motor  and  moved  engines,  and  (2)  the  cost  of 
the  conducting  systems. 

The  motor  and  moved  engines  being  in  practice  iden- 
tical, the  consideration  of  one  suffices  for. both.  These 
machines,  as  has  been  shown,  are  very  simple  in  con- 
struction, and  consist  essentially  of  so  much  cast-iron  and 
insulated  copper  wire,  the  market  prices  of  which  are 
known,  so  that  the  cost  of  any  machine  for  developing  so 
much  horse-power  may  be  easily  calculated.  The  labour 
of  construction  should  form  an  unimportant  item,  for  none 
of  the  skill  is  involved  such  as  is  required  in  the  con- 
struction of  even  the  most  common  steam,  air,  or  gas- 
engine.  The  quantities  of  materials  required  are  but 
little,  if  more,  costly,  in  the  case  of  electric  machines, 
and  this  excess  of  cost  is  due.  to  infrequency  of  de- 
mand. The  construction  of  machines  of  size  hitherto 
unattempted  is  not  required,  and  it  has  been  shown  by 
Prof.  Thomson  that  electric  machines  of  1000  HP.,  as 
proposed  by  Dr.  Siemens,  are  not  necessary,  so  that  there 
would  be  no  need  to  attempt  to  refute  the  question  of  cost 
of  so  unusually  large-sized  engine  as  of  that  Mr.  Sprague  has 
entered  into.  It  has  been  shown  that  ten  100- HP.  engines 
would  give  better  results  as  regards  efficiency,  whilst  at 
the  same  time  it  would  be  nearly  impossible  that  all  the 
machines  could  fall  out  of  repair  simultaneously. 

The  arrangements  of  machines  being  thus  consonant  with 
the  use  of  a  small  conductor,  as  shown  in  the  previous  pages, 
there  is  the  further  advantage  in  laying  this  conductor, 
that  no  air  or  water-tight  joints  have  to  be  made.  Taking 
such  joints  into  consideration,  it  would  be  easy  to  show  by 
figures  that  an  efficiently  insulated  electric  conductor  to 
transmit  the  same  power  could  be  laid  at  less  cost  than  with 
air  or  water,  and  certainly  less  than  with  gas  pipes. 

The  advantages  of  electric  transmission,  it  is  to  be 
hoped,  are  worthy  therefore  of  the  attention  of  every 
engineer  interested  in  transmitting  power. 


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HURST,  C.E.  Twelfth  edition,  thoroughly  revised  and  re-written. 
Royal  32mo,  roan,  $j.  CONTAINING  : 

Formulae  and  Tables  for  the  Strength  of  Materials,  Roofs,  Water  Supply,  Drainage,  Gas, 
and  other  matters  useful  to  Architects  and  Builders — Information  connected  with  Sanitary 
Engineering — Memoranda  on  the  several  Trades  used  in  Building,  including  a  Description  of 
Materials  and  Analyses  for  Prices  of  Builders'  Work — The  Practice  of  Builders'  Measure- 
ment— Mensuration  and  the  Division  of  Land— Tables  of  the  Weights  of  Iron  and  other 
Building  Materials — Constants  of  Labour — Valuation  of  Property— Summary  of  the  Practice 
in  Dilapidations — Scale  of  Professional  Charges  for  Architects  and  Surveyors — Tables  of 
English  and  French  Weights  and  Measures. 

"  It  is  no  disparagement  to  the  many  excellent  publications  we  refer  to,  to  say  that  in  our 
opinion  this  little  pocket-book  of  Hurst's  is  the  very  best  of  them  all,  without  any  exception. 
It  would  be  useless  to  attempt  a  recapitulation  of  the  contents,  for  it  appears  to  contain  almost 
everything  that  anyone  connected  with  building  could  require,  and,  best  of  all,  made  up  in  a 
compact  form  for  carrying  in  the  pocket,  measuring  only  5  in.  by  3  in.,  and  about  \  in.  thick, 
in  a  limp  cover.  We  congratulate  the  author  on  the  success  of  his  laborious  and  practically 
compiled  little  book,  which  has  received  unqualified  and  deserved  praise  from  every  profes- 
sional person  to  whom  we  have  shown  it."—  Ut£  Dublin  Builder, 

A  Treatise  on  the  Use  of  Belting  for  the  Trans- 
mission of  Power ;  with  numerous  Illustrations  of  approved  and  actual 
methods  of  arranging  Main  Driving  and  Quarter-Twist  Belts,  and  of  Belt 
Fastenings.  Examples  and  Rules  in  great  number  for  Exhibiting  and 
Calculating  the  Size  and  Driving  Power  of  Belts.  Plain,  Particular,  and 
Practical  Directions  for  the  Treatment,  Care,  and  Management  of  Belts. 
Descriptions  of  many  varieties  of  Beltings,  together  with  chapters  on  the 
Transmission  of  Power  by  Ropes  ;  by  Iron  and  Wood  Frictional  Gearing ; 
on  the  Strength  of  Belting  Leather  ;  and  on  the  Experimental  Investiga- 
tions of  Morin,  Briggs,  and  others  for  determining  the  Friction  of  Belts 
under  different  Tensions,  which  are  presented  clearly  and  fully,  with  the 
Text  and  Tables  unabridged.  By  JOHN  H.  COOPER,  M.E.  I  vol.,  demy 
8vo,  cloth,  15^. 

Researches  on  the  Action  of  the  Blast  Furnace.     By 

CHARLES  SCHINZ.  Translated  from  the  German  by  W.  H.  Maw  and 
Moritz  Miiller.  Plates,  crown  8vo,  cloth,  8s.  6d. 

Spans  Builders  Pocket-Book  of  Prices  and  Memo- 
randa. Edited  by  W.  YOUNG,  Architect.  Royal  321110,  roan,  41.  6d.  ; 
or  cloth,  red  edges,  3-r.  6d.  Published  annually.  Sixth  edition  now 
ready. 


PUBLISHED  BY  E.  &  F.  N.  SPON.  3 

Long-Span  Railway  Bridges,  comprising  Investiga- 
tions of  the  Comparative  Theoretical  and  Practical  Advantages  of  the 
various  adopted  or  proposed  Type  Systems  of  Construction,  with  numerous 
Formulae  and  Tables  giving  the  weight  of  Iron  or  Steel  required  in 
Bridges  from  300  feet  to  the  limiting  Spans  ;  to  which  are  added  similar 
Investigations  and  Tables  relating  to  Short-span  Railway  Bridges.  Second 
and  revised  edition.  ByB.  BAKER,  Assoc.  Inst.  C.E.  Plates,  crown  8vo, 
cloth,  5.5-. 

The  Builder  s  Clerk ;  a  Guide  to  the  Management 

of  a  Builder's  Business.     By  THOMAS  BALES.     Fcap.  8vo,  cloth,  is.  6d. 

The  Cabinet  Maker ;  being  a  Collection  of  the  most 

approved  Designs  in  the  Mediaeval,  Louis-Seize,  and  Old-English  styles, 
for  the  use  of  Cabinet  Makers,  Carvers,  etc.  By  R.  CHARLES.  96 plates, 
folio,  half-bound,  2is. 

The    Elementary     Principles    of    Carpentry.        By 

THOMAS  TREDGOLD.  Revised  from  the  original  edition,  and  partly 
re-written,  by  JOHN  THOMAS  HURST.  Contained  in  517  pages  of  letter- 
press, and  illustrated  with  48  plates  and  150  -wood  engravings.  Second 
edition,  crown  8vo,  cloth,  iSs. 

Section  I.  On  the  Equality  and  Distribution  of  Forces  —  Section  II.  Resistance  of 
Timber  —  Section  III.  Construction  of  Floors  —  Section  IV.  Construction  of  Roofs  —  Sec- 
tion V.  Construction  of  Domes  and  Cupolas — Section  VI.  Construction  of  Partitions — 
Section  VII.  Scaffolds,  Staging,  and  Gantries — Section  VIII.  Construction  of  Centres  for 
Bridges— Section  IX.  Coffer-dams,  Shoring,  and  Strutting— Section  X.  Wooden  Bridges 
and  Viaducts — Section  XI.  Joints,  Straps,  and  other  Fastenings — Section  XII.  Timber. 

•"A  considerable  time  having  elapsed  since  the  publication  of  the  second  edition  of  this 
work,  which  was  the  last  that  had  been  revised  by  the  author,  his  death  occurring  soon  after, 
a  new  edition  that  would  embrace  recent  improvements  and  examples  was  much  required. 
Our  stock  of  knowledge  regarding  the  strength  of  materials  has  been  largely  increased,  owing 
to  the  labours  of  Hodgkinson,  Kirkaldy,  and  others.  The  rapid  development  of  the  railway 
system  throughout  the  world  has  contributed  greatly  to  the  introduction  of  new  methods  and 
to  the  multiplication  of  examples  in  the  art  of  construction.  More  perfect  and  scientific 
appliances  in  the  erection  of  large  works  have  been  substituted  for  the  primitive  methods  used 
in  the  last  generation.  These  have  all  tended  more  or  less  to  tax  the  ability  and  knowledge 
•of  the  carpenter.  The  opening  up  and  development  of  the  resources  of  new  countries  have 
introduced  varieties  of  timber,  many  of  them  possessing  useful  properties,  not  the  least  of 
which  is.  that  of  resisting  the  attack  of  sea-worms  and  insects — a  cause  of  destruction  that  has 
hitherto  been  a  source  of  much  anxiety  to  the  Profession. 

"  In  order  to  adapt  this  work  as  far  as  possible  to  the  requirements  of  the  modern 
carpenter,  it  has  been  necessary  to  re-write  the  articles  on  Pillars,  Bridges,  and  Timber ;  to 
add  new  sections  on  Coffer-Dams,  Scaffolds,  etc.,  and  to  revise  the  remainder  of  the  work 
throughout.  And  for  the  more  complete  illustration  of  these  subjects  several  new  plates  and 
woodcuts  have  been  added. 

"The  Editor  trusts  that  this  edition  will  merit  the  confidence  of  the  Profession  as  a  book  of 
reference,  and  afford  at  the  same  time  valuable  assistance  to  the  student." 

Engineering  Notes.     By  FRANK  ROBERTSON,  Fellow 

Roy.  Astron.  So<x,  late  first  Lieut.  R.E.,  and •' Civil  Engineer  Public 
Works  Department  in  India.  8vo,  cloth,  12s.  6d. 

The  object  of  this  work  is  to  supply  an  exhaustive  digest  of  all  that  is  known  on  each 
subject,  so  far  as  is  necessary  and  sufficient  for  an  Engineer  in  practice,  especially  in  India. 

B   2 


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A    Practical    Treatise   on    Casting  and   Founding, 

including  descriptions  of  the  modern  machinery  employed  in  the  art.  By 
N.  E.  SPRETSON,  Engineer.  With  82  plates  drawn  to  scale,  412  pp. 
Demy  8vo,  cloth,  iSs. 

A  Pocket-Book  for  Chemists,  Chemical  Manufacturer^ 

Metallurgists,  Dyers,  Distillers,  Brewers,  Sugar  Refiners,  Photographers, 
Students,  etc.,  etc.  By  THOMAS  BAYLEY,  Assoc.  R.C.  Sc.  Ireland,  Ana- 
lytical and  Consulting  Chemist,  Demonstrator  of  Practical  Chemistry, 
Analysis,  and  Assaying,  in  the  Mining  School,  Bristol.  Royal  32mo, 
roan,  gilt  edges,  5^. 

SYNOPSIS  OF  CONTENTS  : 

Atomic  Weights  and  Factors — Useful  Data — Chemical  Calculations — Rules  for  Indirect 
Analysis — Weights  and  Measures  —  Thermometers  "and  Barometers  —  Chemical  Physics  — 
Boiling  Points,  etc. — Solubility  of  Substances — Methods  of  Obtaining  Specific  Gravity — Con- 
version of  Hydrometers — Strength  of  Solutions  by  Specific  Gravity — Analysis — Gas  Analysis — 
Water  Analysis— Qualitative  Analysis  and  Reactions— Volumetric  Analysis— Manipulation- 
Mineralogy  —  Assaying  —  Alcohol  —  Beer  —  Sugar  —  Miscellaneous  Technological  matter 
relating  to  Potash,  Soda,  Sulphuric  Acid,  Chlorine,  Tar  Products,  Petroleum,  Milk,  Tallow, 
Photography,  Prices,  Wages,  etc.,  etc. 

A  Practical  Treatise  on  Coal  Mining.     By  GEORGE 

G.  ANDRE,  F.G.S.,  Assoc.  Inst.  C.E..,  Member  of  the  Society  of  Engineers, 
with  82  lithographic  plates.  2  vols.,  royal  410,  cloth,  3/.  12s. 

CONTENTS : 

I.  Practical  Geology — II.  Coal,  its  Mode  of  Occurrence,  Composition,  and  Varieties — III. 
Searching  for  Coal— IV.  Shaft-sinking— V.  Driving  of  Levels,  or  Narrow  Work— VI.  Systems 
of  Working— VII.  Getting  the  Coal— VIII.  Haulage— IX.  Windine— X.  Drainage— XI. 
Ventilation— XII.  Incidental  Operations— XIII.  Surface  Work— XIV.  Management  and 
Accounts — XV.  Characteristics  of  the  Coal  Fields  of  Great  Britain  and  America. 

Spons*  Information  for  Colonial  Engineers.     Edfted 

by  J.  T.  HURST.    Demy  8vo,  sewed. 

No.  i,  Ceylon.    By  ABRAHAM  DEANE,  C.E.    2s.  6d. 
CONTENTS  : 

Introductory  Remarks  —  Natural  Productions  —  Architecture  and  Engineering  —  Topo- 
graphy, Trade,  and  Natural  History — Principal  Stations— Weights  and  Measures,  etc.,  etc. 

No.  2.  Southern  Africa,  including  the  Cape  Colony,  Natal,  and  the 
Dutch  Republics.  By  HENRY  HALL,  F.R.G.S.,  F.R.C.I.  With 
Map.  3J.  6d.  CONTENTS  : 

General  Description  of  South  Africa — Physical  Geography  with  reference  to  Engineering 
Operations — Notes  on  Labour  and  Material  in  Cape  Colony — Geological  Notes  on  Rock 
Formation  in  South  Africa — Engineering  Instruments  for  Use  in  South  Africa — Principal 
Public  Works  in  Cape  Colony:  Railways,  Mountain  Roads  and  Passes,  Harbour  Works^ 
Bridges,  Gas  Works,  Irrigation  and  Water  Supply,  Lighthouses,  Drainage  and  Sanitary 
Engineering,  Public  Buildings,  Mines — Table  of  Woods  in  South  Africa — Animals  used  for 
Draught  Purposes — Statistical  Notes — Table  of  Distances — Rates  of  Carriage,  etc. 

No.  3.  India.  B^  F.  C.  DANVERS,  Assoc.  Inst.  C.E.  With  Map.  4*.  6d~ 
CONTENTS  : 

Physical  Geography  of  India — Building  Materials— Roads— Railways — Bridges — Irriga- 
tion—  River  Works  —  Harbours  —  Lighthouse  Buildings  —  Native  Labour — The  Principal 
Trees  of  India — Money— Weights  and  Measures — Glossary  of  Indian  Terms,  etc. 


PUBLISHED  BY  E.  &  F.  N.  SPON. 


The  Clerk  of  Works;  a  Vade  Mecum  for  all  engaged 

in  the  Superintendence  of  Building  Operations.  By  G.  G.  HOSKINS, 
F.R.I.B.A.  Fcap.  8vo,  cloth,  u.  6d. 

Coffee  Planting  in  Southern  India  and  Ceylon.     By 

E.  C.  P.  HULL.     Crown  8vo,  cloth,  $s. 

Tropical  Agriculture;  or,  the  Culture,  Preparation, 

Commerce,  and  Consumption  of  the  Principal  Products  of  the  Vegetable 
Kingdom,  as  furnishing  Food,  Clothing,  Medicine,  etc.,  and  in  their 
relation  to  the  Arts  and  Manufactures ;  forming  a  practical  treatise  and 
Handbook  of  Reference  for  the  Colonist,  Manufacturer,  Merchant,  and 
Consumer,  on  the  Cultivation,  Preparation  for  Shipment,  and  Commercial 
Value,  etc.,  of  the  various  Substances  obtained  from  Trees  and  Plants 
entering  into  the  Husbandry  of  Tropical  and  Sub-Tropical  Regions.  By 
P.  L.  SIMMONDS.  Second  Edition,  revised  and  improved,  in  one  thick 
vol.  8vo,  cloth,  I/,  is. 

Compensations;  a  Text-book  for  Surveyors,  in  tabu- 
lated form.    By  BANISTER  FLETCHER.    Crown  8vo,  cloth,  5.$-. 
CONTENTS  : 

The  Varieties  of  Damage  for  which  Claims  may  arise — Various  Classes  of  Property — 
Points  to  be  observed  in  Surveys — Notices  to  Treat — Nature  of  Damage  for  which  Claims 
can  and  cannot  be  sustained — What  Property  can  be  compulsorily  taken — When  Entry  on 
Property  can  and  cannot  be  compulsorily  madeyOf  Goodwill  and  Stock — and  of  the  various 
Legal  Methods  of  Settlement  of  Disputed  Claims— together  with  Full  and  Explicit  Instruc- 
tions on  the  Methods  of  Valuing  and  of  Making  Claims ;  with  Comments  on  Cases  arising 
under  the  Metropolis  Local  Management  and  Metropolitan  Buildings  Acts ;  the  whole  given 
in  a  Practical  and  Comprehensive  Form,  supplemented  by  a  copious  Appendix,  containing 
many  Useful  Forms  and  Precedents,  and  also  Tables  for  the  Valuation  of  Freeholds,  Lease- 
holds, Reversions,  and  Life- Interests. 

Cotton  Cultivation  in  its  various  details;  the  Barrage 

of  Great  Rivers,  and  Instructions  for  Irrigating,  Embanking,  Draining, 
and  Tilling  Land  in  Tropical  and  other  Countries  possessing  high  thermo- 
metric  temperatures,  especially  adapted  to  the  improvement  of  the  cultural 
soils  of  India.  By  JOSEPH  GIBBS,  Member  Institute  Civil  Engineers. 
With  5  plates.  Crown  8vo,  cloth,  "js.  6d. 

Dilapidations;  a  Text-book  for  Architects  and  Sur- 
veyors, in  Tabulated  Form.  By  BANISTER  FLETCHER,  Fellow  Royal 
Inst.  Brit.  Arch.  (Author  of  *  Model  Houses ' ),  showing  who  are  liable  for 
Dilapidations,  and  the  extent  of  the  liability  of  Lessors,  Lessees,  Tenants 
at  will,  Tenants  by  elegit,  Statute,  Merchant,  or  Staple  Tenants  in  fee 
simple,  Tenants  in  tail,  Tenants  for  life,  Tenants  for  years  without 
impeachment  of  Waste,  Mortgagor,  Mortgagee  in  possession,  Yearly 
Tenants,  Tenants  in  common,  and  joint  Tenants,  Rights  of  coparceners  ; 
also  what  are  dilapidations  and  waste,  and  further  fully  instructs  the 
surveyor  how  to  take  and  value  them,  to  which  is  added  the  duties  of 
surveyors,  with  a  table  of  legal  cases,  embracing  the  most  recent,  and 
illustrated  throughout  by  examples  drawn  from  the  author's  experience, 
and  latest  legal  decisions.  Crown  8vo,  cloth,  5j. 


CATALOGUE  OF  SCIENTIFIC  BOOKS 


Spons  Dictionary  of  Engineering,  Civil,  Mechanical? 

Military,  and  Naval',  with  technical  terms  in  French,  German,  Italian, 
and  Spanish,  3100  pp.,  and  nearly  8000  engravings,  in  super-royal  8vor 
in  8  divisions,  5/.  S.T.  Complete  in  3  vols.,  cloth,  5/.  $s.  Bound  in  a 
superior  manner,  half-morocco,  top  edge  gilt,  3  vols.,  61.  12s. 

A    Treatise  on  the  Origin,  Progress,  Prevention,  and 

Cure  of  Dry  Rot  in  Timber;  with  Remarks  on  the  Means  of  Preserving 
Wood  from  Destruction  by  Sea- Worms,  Beetles,  Ants,  etc.  By  THOMAS 
ALLEN  BRITTON,  late  Surveyor  to  the  Metropolitan  Board  of  Works, 
etc.,  etc.  Plates,  crown  Svo,  cloth,  7^.  6d. 

A  General  Table  for  facilitating  the  Calculation  of 

Earthworks  for  Railways,  Canals,  etc. ;  with  a  Table  of  Proportional 
Parts.  By  FRANCIS  BASHFORTH,  M.A.,  Fellow  of  St.  John's  College, 
Cambridge.  In  Svo,  cloth,  with  mahogany  slide,  4$-. 

"  This  little  volume  should  become  the  handbook  of  every  person  whose  duties  require  even 
occasional  calculations  of  this  nature  :  were  it  only  that  it  is  more  extensively  applicable  than 
any  other  in  existence,  we  could  cordially  recommend  it  to  our  readers  ;  but  when  they  learn 
that  the  use  of  it  involves  only  half  the  labour  of  all  other  Tables  constituted  for  the  same 
purposes,  we  offer  the  strongest  of  all  recommendations— that  founded  on  the  value  of  time."— • 
Mechanic's  Magazine. 

A  General  Sheet  Table  for  facilitating  the  Calculation 

of  Earthworks.     By  F.  BASHFORTH,  M.A.     6</. 

A    Handbook   of   Electrical    Testing.      By   H.     R. 

KEMPE,  Assoc.  of  the  Society  of  Telegraph  Engineers.  Fcap.  8vo, 
cloth,  5^. 

Electricity;  its  Theory,  Sources,  and  Applications. 

By  JOHN  T.  SPRAGUE,  Member  of  the  Society  of  Telegraph  Engineers. 
With  91  woodcuts  and  30  valuable  Tables.  Crown  Svo,  cloth,  8.r. 

Electricity  and  the  Electric  Telegraph.     By  GEORGE 

B.  PRESCOTT.     With  564  woodcut  illustrations,  Svo,  cloth,  iSs. 

Electro -Telegraphy.      By  FREDERICK   S.    BEECHEY, 

Telegraph  Engineer,  a  Book  for  Beginners.     Fcap.  Svo,  cloth,  is.  6d. 

Engineering  Papers.      By    GRAHAM    SMITH.      Svo, 

cloth,  $s.  CONTENTS: 

Mortar:  "Miller  Prize"  Paper— Practical  Ironwork  :  "  Miller  Prize  "  Paper— Retaining 
Walls:  Paper  read  at  the  Edinburgh  and  Leith  Engineers'  Society.  With  Addenda  and 
Discussions  to  each. 

Spons  Engineers  and  Contractors   Illustrated  Book 

of  Prices  of  Machines,  Tools,  Ironwork,  and  Contractors'1  Material. 
Royal  Svo,  cloth,  'js.  6d. 

The  Gas    Consumers   Handy  Book.     By  WILLIAM 

RICHARDS,  C.E.     i8mo,  sewed,  6d. 


PUBLISHED  BY  E.  &  F.  N.  SPON. 


A  Pocket-Book  of  Use/id  Formidce  and  Memoranda 

for  Civil  and  Mechanical  Engineers.  By  GUILFORD  L.  MOLESWORTH, 
Mem.  Ins.  C.  E.,  Consulting  Engineer  to  the  Government  of  India  for 
State  Railways.  Nineteenth  edition,  with  a  valuable  contribution  on 
Telegraphs  by  R.  S.  BROUGH  and  Dr.  PAGET  HIGGS.  32mo,  roan,  6s. 
Ditto,  interleaved  with  ruled  Paper  for  Office  use,  gs.  Ditto,  printed  on 
India  paper,  6s.  SYNOPSIS  OF  CONTENTS: 

Surveying,  Levelling,  etc. — Strength  and  Weight  of  Materials — Earthwork,  Brickwork, 
Masonry,  Arches,  etc. — Struts,  Columns,  Beams,  and  Trusses — Flooring,  Roofing,  and  Roof 
Trusses — Girders,  Bridges,  etc. — Railways  and  Roads — Hydraulic  Formulae — Canals,  Sewers, 
Waterworks,  Docks — Irrigation  and  Breakwaters — Gas,  Ventilation,  and  Warming — Heat, 
Light,  Colour,  and  Sound — Gravity :  Centres,  Forces,  and  Powers — Millwork,  Teeth  of 
Wheels,  Shafting,  etc. — Workshop  Recipes — Sundry  Machinery — Animal  Power — Steam  and 
the  Steam  Engine — Water-power,  Water-wheels,  Turbines,  etc. — Wind  and  Windmills — 
Steam  Navigation,  Ship  Building,  Tonnage,  etc. — Gunnery,  Projectiles,  etc. — Weights, 
Measures,  and  Money — Trigonometry,  Conic  Sections,  and  Curves— Telegraphy — Mensura- 
tion— Tables  of  Areas  and  Circumference,  and  Arcs  of  Circles — Logarithms,  Square  and 
Cube  Roots,  Powers — Reciprocals,  etc. — Useful  Numbers — Differential  and  Integral  Calcu- 
lus— Algebraic  Signs — Telegraphic  Construction  and  Formulae. 

"  Most  of  our  readers  are  already  acquainted  with  Molesworth's  Pocket-book,  and  not  a 
few,  we  imagine,  are  indebted  to  it  for  valuable  information,  or  for  refreshers  of  the  memory. 
The  book  has  been  re-arranged,  the  supplemental  formulas  and  tables  added  since  the  first 
issue  having  now  been  incorporated  with  the  body  of  the  book  in  their  proper  positions,  the 
whole  making  a  handy  size  for  the  pocket.  Every  care  has  been  taken  to  ensure  correctness, 


both  clerically  and  typographically,  and  the  book  is  an  indispensable  vade-mecum  for  the 
id  the  professional  man."— English  Mechanic. 


mechanic  anc 


Spons     Tables    and   Memoranda    for    Engineers; 

selected  and  arranged  by  J.  T.  HURST,  C.E.,  Author  of  'Architectural 
Surveyors'  Handbook,'  'Hurst's  Tredgold's  Carpentry,'  etc.  641110,  roan, 
gilt  edges,  third  edition,  revised  and  improved,  is.  Or  in  cloth  case, 
is.  6d. 

This  work  is  printed  in  a  pearl  type,  and  is  so  small,  measuring  only  z£  in.  by  if  in.  by 
i  in.  thick,  that  it  may  be  easily  carried  in  the  waistcoat  pocket. 

"  It  is  certainly  an  extremely  rare  thing  for  a  reviewer  to  be  called  upon  to  notice  a  volume 
measuring  but  23  in.  by  if  in.,  yet  these  dimensions  faithfully  represent  the  size  of  the  handy 
little  book  before  us.  The  volume — which  contains  118  printed  pages,  besides  a  few  blank 
pages  for  memoranda— is,  in  fact,  a  true  pocket-book,  adapted  for  being  carried  in  the  waist- 
coat pocket,  and  containing  a  far  greater  amount  and  variety  of  information  than  most  people 

would  imagime  could  be  compressed  into  so  small  a  space The  little  volume  has  been, 

compiled  with  considerable  care  and  judgment,  and  we  can  cordially  recommend  it  to  our 
readers  as  a  useful  little  pocket  companion." — Engineering. 

The    French- Polisher s  Manual.       By   a    French- 

Polisher;  containing  Timber  Staining,  Washing,  Matching,  Improving, 
Painting,  Imitations,  Directions  for  Staining,  Sizing,  Embodying, 
Smoothing,  Spirit  Varnishing,  French-Polishing,  Directions  for  Re- 
polishing.  Third  edition,  royal  32mo,  sewed,  6d. 

Analysis,  Technical  Valuation,  Purification  and  Use 

of  Coal  Gas.  By  the  Rev.  W.  R.  BOWDITCH,  M.  A.  With  wood  engravings, 
8vo,  cloth,  12s.  6d. 

Condensation  of  Gas— Purification  of  Gas— Light— Measuring— Place  of  Testing  Gas- 
Test  Candles — The  Standard  for  Measuring  Gas-light — Test  Burners — Testing  Gas  for 
Sulphur — Testing  Gas  for  Ammonia — Condensation  by  Bromine — Gravimetric  Method  of 
taking  Specific  Gravity  of  Gas — Carburetting  or  Naphthalizing  Gas — Acetylene — Explosions 
of  Gas — Gnawing  of  Gaspipes  by  Rats — Pressure  as  related  to  Public  Lighting,  etc. 


CATALOGUE  OF  SCIENTIFIC  BOOKS 


A  Practical  Treatise  on  the  Manufacture  and  Distri- 
bution of  Coal  Gas.  By  WILLIAM  RICHARDS.  Demy  410,  with  numerous 
wood  engravings  and  large  plates,  cloth,  28^. 

SYNOPSIS  OF  CONTENTS. 

Introduction— History  of  Gas  Lighting  —  Chemistry  of  Gas  Manufacture,  by  Lewis 
Thompson,  Esq.,  M.R.C.S. — Coal,  with  Analyses,  by  J.  Paterson,  Lewis  Thompson,  and 
G.  R.  Hislop,  Esqrs. — Retorts,  Iron  and  Clay — Retort  Setting — Hydraulic  Main — Con- 
densers—Exhausters— Washers  and  Scrubbers— Purifiers  —  Purification  —  History  of  Gas 
Holder  —  Tanks,  Brick  and  Stone,  Composite,  Concrete,  Cast-iron,  Compound  Annular 
Wrpught-iron  —  Specifications  —  Gas  Holders  —  Station  Meter  —  Governor  —  Distribution — 
Mains — Gas  Mathematics,  or  Formulae  for  the  Distribution  of  Gas,  by  Lewis  Thompson,  Esq.— 
Services — Consumers'  Meters— Regulators— Burners— Fittings— Photometer— Carburization 
of  Gas— Air  Gas  and  Water  Gas — Composition  of  Coal  Gas,  by  Lewis  Thompson,  Esq. — 
Analyses  of  Gas — Influence  of  Atmospheric  Pressure  and  Temperature  on  Gas— Residual 
Products— Appendix — Description  of  Retort  Settings,  Buildings,  etc.,  etc. 

Practical  Geometry  and  Engineering  Drawing ;    a 

Course  of  Descriptive  Geometry  adapted  to  the  Requirements  of  the 
Engineering  Draughtsman,  including  the  determination  of  cast  shadows 
and  Isometric  Projection,  each  chapter  being  followed  by  numerous 
examples ;  to  which  are  added  rules  for  Shading  Shade-lining,  etc., 
together  with  practical  instructions  as  to  the  Lining,  Colouring,  Printing, 
and  general  treatment  of  Engineering  Drawings,  with  a  chapter  on 
drawing  Instruments.  By  GEORGE  S.  CLARKE,  Lieut.  R.E.,  Instructor 
in  Mechanical  Drawing,  Royal  Indian  Engineering  College,  Cooper's 
Hill.  20  plates,  410,  cloth,  15^. 

The  Elements   of    Graphic   Statics.     By   Professor 

KARL  VON  OTT,  translated  from  the  German  by  G.  S.  CLARKE,  Lieut. 
R.E.,  Instructor  in  Mechanical  Drawing,  Royal  Indian  Engineering 
College,  Cooper's  Hill.  Crown  8vo,  cloth,  5^. 

A    Practical    Treatise  on   Heat,   as  applied  to   the 

Useful  Arts',  for  the  Use  of  Engineers,  Architects,  etc.  By  THOMAS 
Box.  Second  edition,  revised  and  enlarged,  crown  8vo,  cloth,  12s.  6d. 

Hints   to    Young  Engineers.      By  J.    W.   WILSON, 

A.I.C.E.,  Principal  of  the  Crystal  Palace  School  of  Engineering.  I2mo, 
sewed,  6</. 

The  New  Formula  for  Mean  Velocity  of  Discharge 

of  Rivers  and  Canals.  By  W.  R.  KUTTER,  translated  from  articles  in 
the  '  Cultur-Ingenieur.'  By  Lowis  D'A.  JACKSON,  Assoc.  Inst.  C.E. 
8vo,  cloth,  I2s.  6d. 

Office  Hydraulic  Tables ;  for  the  use  of  Engineers 

engaged  in  Waterworks,  giving  the  Discharge  and  Dimensions  of  Rivers, 
Channels,  and  Pipes.  By  J.  NEVILLE.  On  a  large  folio  sheet,  is. 

Hydraidics  of  Great  Rivers  ;  being  Observations  and 

Surveys  on  the  Largest  Rivers  of  the  World.  By  J.  J.  REVY.  Imp.  410, 
cloth,  with  eight  large  plates  and  charts,  2l.  2s. 


PUBLISHED  BY  E.  &  F.  N.  SPON. 


Hops,    their    Cultivation,    Commerce,    and    Uses   in 

various  Countries.     By  P.  L.  SiMMONDS.     Cown  8vo,  cloth,  4*.  6d. 

Practical  Hydraulics  ;  a  Series  of  Rules  and  Tables 

for  the  use  of  Engineers,  etc.,  etc.  By  THOMAS  Box.  Fourth  edition, 
numerotis  plates,  post  8vo,  cloth,  5-r. 

Tke  Indicator  Diagram  Practically  Considered.     By 

N.  P.  BURGH,  Engineer.  Numerous  illustrations,  fifth  edition.  Crown 
8vo,  cloth,  6s.  6d. 

"  This  volume^  possesses  one  feature  which  renders  it  almost  unique ;  this  feature  is  the 
mode  in  which  it  is  illustrated.  It  is  not  difficult  to  take  a  diagram  if  the  instrument  is  once 
set,  and  the  setting  with  stationary  engines  is  occasionally  easy  enough,  but  circumstances 
continually  arise  under  which  the  young  engineer  is  completely  at  a  loss  as  to  how  to  obtain 
a  diagram.  All  uncertainty  will  be  removed  by  referring  to  the  book  under  consideration : 
here  we  have  drawings  of  the  arrangements  to  be  adopted  under  every  conceivable  circum- 
stance, drawings,  we  may  add,  illustrating  the  practice  of  the  best  engineers  of  the  day." — 
Engineer. 

Link- Motion  and  Expansion  Gear  Practically  Con- 
sidered. By  N.  P.  BURGH,  Engineer.  Illustrated  -with  90  plates  and  229 
wood  engravings,  small  4to,  handsomely  half-bound  in  morocco,  2/.  2s. 

The   Mechanician   and   Constructor  for  Engineers, 

comprising  Forging,  Planing,  Lining,  Slotting,  Shaping,  Turning,  Screw 
Cutting,  etc.  By  CAMERON  KNIGHT.  Containing  ^plates,  1147  illus- 
trations, and  iff]  pages  of  letterpress,  410,  half-morocco,  2/.  12s.  6d. 

T/ie   Essential  Elements  of   Practical   Mechanics; 

based  on  the  Principle  of  Work,  designed  for  Engineering  Students.  By 
OLIVER  BYRNE,  formerly  Professor  of  Mathematics,  College  for  Civil 
Engineers.  Second  edition,  illustrated  by  numerous  -wood  engravings, 
post  8vo,  cloth,  is.  6d. 

CONTENTS : 

Chap.  I.  How  Work  is  Measured  by  a  Unit,  both  with  and  without  reference  to  a  Unit 
of  Time — Chap.  2.  The  Work  of  Living  Agents,  the  Influence  of  Friction,  and  introduces 
one  of  the  most  beautiful  Laws  of  Motion— Chap.  J.  The  principles  expounded  in  the  first  and 
second  chapters  are  applied  to  the  Motion  of  Bodies — Chap.  4.  The  Transmission  of  Work  by 
simple  Machines— Chap.  5.  Useful  Propositions  and  Rules. 

The  Practical  Millwright's  and  Engineers  Ready 

Reckoner;  or  Tables  for  finding  the  diameter  and  power  of  cog-wheels, 
diameter,  weight,  and  power  of  shafts,  diameter  and  strength  of  bolts,  etc. 
By  THOMAS  DIXON.  Fourth  edition,  I2ino,  cloth,  3-r. 

CONTENTS: 

Diameter  and  Power  of  Wheels— Diameter,  Weight,  and  Power  of  Shafts— Multipliers  for 
Steam  used  Expansively— Diameters  and  Strength  of  Bolts — Size  and  Weight  of  Hexagonal 
Nuts — Speed  of  Governors  for  Steam  Engines— Contents  of  Pumps — Working  Barrels — Cir- 
cumferences and  Areas  of  Circles — Weight  of  Boiler  Plates — French  and  English  Weights  and 
Measures,  etc. 


io  CATALOGUE  OF  SCIENTIFIC  BOOKS 


The  Principles  of  Mechanics  and  their  Application  to 

Prime  Movers,  Naval  Architecture,  Iron  Bridges,  Water  Supply,  etc.  By 
W.  J.  MILLAR,  C.E.,  Secretary  to  the  Institution  of  Engineers  and  Ship- 
builders, Scotland.  Crown  8vo,  cloth,  qs.  6d. 

A  Practical  Treatise  on  Mill-gearing,  Wheels,  Shafts, 

Riggers,  etc.',  for  the  use  of  Engineers.  By  THOMAS  Box.  Crown  8vo, 
cloth,  second  edition,  7^.  6d. 

Mining  Machinery;  a  Descriptive  Treatise  on  the 

Machinery,  Tools,  and  other  Appliances  used  in  Mining.  By  G.  G. 
ANDRE,  F.G.S.,  Assoc.  Inst.  C.E.,  Mem.  of  the  Society  of  Engineers. 
Royal  4to,  uniform  with  the  Author's  Treatise  on  Coal  Mining,  con- 
taining 182  plates,  accurately  drawn  to  scale,  with  descriptive  text,  ia 
2  vols.,  cloth,  s/.  i2j.  CONTENTS: 

Machinery  for  Prospecting,  Excavating,  Hauling,  and  Hoisting — Ventilation — Pumping — 
Treatment  of  Mineral  Products,  including  Gold  and  Silver,  Copper,  Tin,  and  Lead,  Iron,. 
Coal,  Sulphur,  China  Clay,  Brick  Earth,  etc. 

The  Pattern  Makers  Assistant ;  embracing  Lathe 

Work,  Branch  Work,  Core  Work,  Sweep  Work,  and  Practical  Gear 
Construction,  the  Preparation  and  Use  of  Tools,  together  with  a  lanje 
collection  of  Useful  and  Valuable  Tables.  By  JOSHUA  ROSE,  M.E. 
With  250  ilhistrations.  Crown  8vo,  cloth,  los.  6d. 

The  Science  and  Art  of  the  Manufactitre  of  Portland 

Cement,  with  observations  on  some  of  its  constructive  applications,  'with 
numerous  illustrations.  By  HENRY  REID,  C.E.,  Author  of  'A  Practical 
Treatise  on  Concrete,'  etc.,  etc.  8vo,  cloth,  iSs. 

The  Draughtsman  s  Handbook  of  Plan  and  Map 

Drawing',  including  instructions  for  the  preparation  of  Engineering, 
Architectural,  and  Mechanical  Drawings.  With  numerous  illustrations' 
in  the  text,  and  33  plates  (15  printed  in  colours'].  By  G.  G.  ANDRK, 
F.G.S.,  Assoc.  Inst.  C.E.  4to,  cloth,  15^. 

CONTENTS  : 

The  Drawing  Office  and  its  Furnishings — Geometrical  Problems — Lines,  Dots,  and  their 
Combinations — Colours,  Shading,  Lettering,  Bordering,  and  North  Points — Scales — Plotting 
—Civil  Engineers'  and  Surveyors'  Plans — Map  Drawing — Mechanical  and  Architectural 
Drawing — Copying  and  Reducing  Trigonometrical  Formulae,  etc.,  etc. 

The  Railway  Builder ;  a  Handbook  for  Estimating- 

the  Probable  Cost  of  American  Railway  Construction  and  Equipment. 
By  WILLIAM  J.  NICOLLS,  Civil  Engineer.  Illustrated,  full  bound,  pocket- 
book  form,  *]s.  6d. 

Rock  Blasting:   a  Practical  Treatise  on  the  means 

employed  in  Blasting  Rocks  for  Industrial  Purposes.  By  G.  G.  ANDRE, 
F.G.S.,  Assoc.  Inst.  C.E.  With  56  illustrations  and  12 plates,  8vo,  cloth, 
los.  6d. 


PUBLISHED  BY  E.  &  F.  N.  SPON.  ii 


Surcharged  and  different  Forms  of  Retaining  Walls. 

By  J.  S.  TATE.     Cuts,  8vo,  sewed,  2s. 

A  Treatise  on  Ropemaking  as  practised  in  public  and 

private  Rope-yards,  with  a  Description  of  the  Manufacture,  Rules,  Tables 
of  Weights,  etc.,  adapted  to  the  Trade,  Shipping,  Mining,  Railways, 
Builders,  etc.  By  R.  CHAPMAN,  formerly  foreman  to  Messrs.  Hudclart 
and  Co.,  Limehouse,  and  late  Master  Ropemaker  to  H.M.  Dockyard, 
Deptford.  Second  edition,  12  mo,  cloth,  3^. 

Sanitary  Engineering  ;   a  Series  of  Lectures  given 

before  the  School  of  Engineering,  Chatham.  Division  I.  Air. — Division  II. 
Water.  —  Division  III.  The  Dwelling.  —  Division  IV.  The  Town  and 
Village. — Division  V.  The  Disposal  of  Sewage.  Copiously  illustrated. 
By  J.  BAILEY  DENTON,  C.E.,  F.G.S.,  Honorary  Member  of  the  Agri- 
cultural Societies  of  Norway,  Sweden,  and  Hanover,  and  Author  of  the 
'Farm  Homesteads  of  England,'  'Village  Sanitary  Economy,'  'Storage 
of  WTater,'  'Sewage  Farming,'  etc.  Royal  8vo,  cloth,  25^. 

Sanitary  Engineering;   a  Guide  to  the  Construction 

of  Works  of  Sewerage  and  House  Drainage,  with  Tables  for  facilitating 
the  calculations  of  the  Engineer.  By  BALDWIN  LATHAM,  C.E.,  M.  Inst. 
C.E.,  F.G.S.,  F.M.S.,  Past-President  of  the  Society  of  Engineers.  Second 
edition,  with,  numerous  plates  and  woodcuts,  8vo,  cloth,  il.  los. 

Cleaning  and  Scouring ;  a  Manual  for  Dyers,  Laun- 
dresses, and  for  Domestic  Use.    By  S.  CHRISTOPHER.     i8mo,  sewed,  6d. 

A  Practical    Treatise  on  modern  Screw-Propulsion. 

By  N.  P.  BURGH,  Engineer.  Illustrated  with  52  large  plates  and  103 
woodcuts,  410,  half- morocco,  2/.  2s. 

Screw  Cutting  Tables  for  Engineers  and  Machinists, 

giving  the  values  of  the  different  trains  of  Wheels  required  to  produce 
Screws  of  any  pitch,  calculated  by  Lord  Lindsay,  M.P.,  F.R.S.,  F.R.A.S., 
etc.  Royal  8vo,  cloth,  oblong,  2.5. 

Screw    Cutting    Tables,   for  the  use  of  Mechanical 

Engineers,  showing  the  proper  arrangement  of  Wheels  for  cutting  the 
Threads  of  Screws  of  any  required  pitch,  with  a  Table  for  making  the 
Universal  Gas-pipe  Threads  and  Taps.  By  W.  A.  MARTIN,  Engineer. 
Second  edition,  royal  8vo,  oblong,  cloth,  is. 

Vazeeri  Rupi,  the  Silver  Country  of  the  Vazeers,  in 

Kulu  :  its  Beauties,  Antiquities,  and  Silver  Mines,  including  a  Trip  over 
the  lower  Himalayah  Range  and  Glaciers.  By  J.  CALVERT,  F.G.S., 
Mem.  Inst.  C.E.  Illustrated  ivith  a  map  and  coloured  plates,  8vo,  cloth, 
i6s. 


12  CATALOGUE  OF  SCIENTIFIC  BOOKS 


A  Treatise  on  a  Practical  Method  of  Designing  Slide 

Valve  Gears  by  Simple  Geometrical  Construction,  based  upon  the  principles 
enunciated  in  Euclid's  Elements,  and  comprising  the  various  forms  of 
Plain  Slide  Valve  and  Expansion  Gearing  ;  together  with  Stephenson's, 
Gooch's,  and  Allan's  Link-Motions,  as  applied  either  to  reversing  or  to 
variable  expansion  combinations.  By  EDWARD  J.  COWLING  WELCH, 
Memb.  Inst.  Mechanical  Engineers.  Crown  8vo,  cloth.  6s. 

The  Slide   Valve  practically  considered.     By  N.   P. 

BURGH,  Engineer.  Seventh  edition,  containing  88  illustrations •,  and 
12.1  pages  of  letterpress,  crown  8vo,  cloth,  $s. 

A  Pocket-Book  for  Boiler  Makers  and  Steam  Users, 

comprising  a  variety  of  useful  information  for  Employer  and  Workman, 
Government  Inspectors,  Board  of  Trade  Surveyors,  Engineers  in  charge 
of  Works  and  Slips,  Foremen  of  Manufactories,  and  the  general  Steam- 
using  Public.  By  MAURICE  JOHN  SEXTON.  Royal  32mo,  roan,  gilt 
edges,  5-r. 

Practical    Treatise   on    Steam    Boilers    and  Boiler 

Making.  By  N.  P.  BURGH,  Mem.  Inst.  Mec.  Eng.  Illustrated  by  1163 
wood  engravings  and  50  large  folding  plates  of  working  drawings,  royal  4to, 
half-morocco,  3/.  13^.  6d. 

Modern  Compound  Engines  ;  being  a  Supplement  to 

Modern  Marine  Engineering.  By  N.  P.  BURGH,  Mem.  Inst.  Mech.  Eng. 
Numerous  large  plates  of  working  drawings,  4to,  cloth,  iSs. 

The  following  Firms  have  contributed  Working  Drawings  of  their  best  and  most  modern 
examples  of  Engines  fitted  in  the  Royal  and  Mercantile  Navies  :  Messrs.  Maudslay,  Rennie , 
Watt,  Dudgeon,  Humphreys,  Ravenhill,  Jackson,  Perkins,  Napier,  Elder,  Laird,  Day, 
Allibon. 

A  Practical  Treatise  on  the  Steam  Engine,  con- 
taining Plans  and  Arrangements  of  Details  for  Fixed  Steam  Engines, 
with  Essays  on  the  Principles  involved  in  Design  and  Construction.  By 
ARTHUR  RIGG,  Engineer,  Member  of  the  Society  of  Engineers  and  of 
the  Royal  Institution  of  Great  Britain.  Demy  4to,  copiously  illustrated 
with  woodcuts  and  96  plates,  in  one  Volume,  half- bound  morocco,  2/.  2s. 

This  work  is  not,  in  any  sense,  an  elementary  treatise,  or  history  of  the  steam  engine,  but 
is  intended  to  describe  examples  of  Fixed  Steam  Engines  without  entering  into  the  wide 
domain  of  locomotive  or  marine  practice.  To  this  end  illustrations  will  be  given  of  the  most 
recent  arrangements  of  Horizontal,  Vertical,  Beam,  Pumping,  Winding,  Portable,  Semi- 
portable,  Corliss,  Allen,  Compound,  and  other  similar  Engines,  by  the  most  eminent  Firms  in 
Great  Britain  and  America.  The  laws  relating  to  the  action  and  precautions  to  be  observed 
in  the  construction  of  the  various  details,  such  as  Cylinders,  Pistons,  Piston-rods,  Connecting- 
rods,  Cross-heads,  Motion-blocks,  Eccentrics,  Simple,  Expansion,  Balanced,  and  Equilibrium 
Slide-valves,  and  Valve-gearing  will  be  minutely  dealt  with.  In  this  connection  will  be  found 
articles  upon  the  Velocity  of  Reciprocating  Parts  and  the  Mode  of  Applying  the  Indicator, 
Heat  and  Expansion  of  Steam  Governors,  and  the  like.  It  is  the  writer's  desire  to  draw 
illustrations  from  every  possible  source,  and  give  only  those  rules  that  present  practice  deems 


PUBLISHED  BY  E.  &  K  N.  SPON.  13 


The  Steam  Engine  considered  as  a  Heat  Engine :  a 

Treatise  on  the  Theory  of  the  Steam  Engine,  illustrated  by  Diagrams, 
Tables,  and  Examples  from  Practice.  By  JAS.  H.  COTTERILL,  M.A., 
Professor  of  Applied  Mechanics  in  the  Royal  Naval  College.  8vo,  cloth, 
12s.  6d. 

Modern  Marine  Engineering  applied  to  Paddle  and 

Screw  Propulsion  ;  consisting  of  36  plates,  259  wood  engravings,  and 
403  pages  of  descriptive  matter,  the  whole  being  an  exposition  of  the 
present  practice  of  the  following  firms  :  Messrs.  J.  Penn  and  Sons  ; 
Maudslay,  Sons,  and  Field  ;  James  Watt  and  Co.  ;  J.  and  G.  Rennie  ; 
R.  Napier  and  Sons  ;  J.  and  W.  Dudgeon ;  Ravenhill  and  Hodgson  ; 
Humphreys  and  Tennant ;  Mr.  J.  F.  Spencer ;  and  Messrs.  Forester  and 
Co.  By  N.  P.  BURGH,  Engineer,  4to,  cloth,  2/.  5*. 

A  Pocket- Book  of  Practical  Rides  for  the  Proportions 

of  Modern  Engines  and  Boilers  for  Land  and  Marine  purposes.  By  N.  P. 
BURGH.  Sixth  edition,  revised,  with  Appendix,  royal  32mo,  roan,  4^.  6d. 

Details  of  High-Pressure  Engine,  Beam  Engine,  Condensing,  Marine  Screw  Engines, 
Oscillating  Engines,  Valves,  etc.,  Land  and  Marine  Boilers,  Proportions  of  Engines  produced 
by  the  Rules.  Proportions  of  Boilers,  etc. 

A   Practical   Treatise  on  the   Science  of  Land  and 

Engineering  Surveying,  Levelling,  Estimating  Quantities,  etc.,  with  a 
general  description  of  the  several  Instruments  required  for  Surveying, 
Levelling,  Plotting,  etc.  By  H.  S.  MERRETT.  41  fine  plates  with  Illus- 
trations and  Tables,  royal  8vo,  cloth,  Jhird  edition,  12s.  6d. 

PRINCIPAL  CONTENTS  : 

Part  i.  Introduction  and  the  Principles  of  Geometry.  Part  2.  Land  Surveying.;  com- 
prising General  Observations— The  Chain— Offsets  Surveying  by  the  Chain  only— Surveying 
Hilly  Ground — To  Survey  an  Estate  or  Parish  by  the  Chain  only — Surveying  with  the 
Theodolite— Mining  and  Town.'  Surveying— Railroad  Surveying— Mapping— Division  and 
Laying  out  of  Land — Observations  on  Enclosures — Plane  Trigonometry.  Part  3.  Levelling — 
Simple  and  Compound  Levelling— The  Level  Book— Parliamentary  Plan  and  Section- 
Levelling  with  a  Theodolite — Gradients — Wooden  Curves— To  Lay  out  a  Railway  Curve — 
Setting  out  Widths.  Part  4.  Calculating  Quantities  generally  for  Estimates — Cuttings  and 
Embankments — Tunnels — Brickwork — Ironwork — Timber  Measuring.  Part  5.  Description 
and  Use  of  Instruments  in  Surveying  and  Plotting — The  Improved  Dumpy  Level — Troughton's 
Level  —  The  Prismatic  Compass  —  Proportional  Compass — Box  ^Sextant — Vernier — Panta- 
graph — Merrett's  Improved  Quadrant — Improved  Computation  Scale — The  Diagonal  Scale — 
Straight  Edge  and  Sector.  Part  6.  Logarithms  of  Numbers  —  Logarithmic  Sines  and 
Co-Sines,  Tangents  and  Co-Tangents — Natural  Sines  and  Co- Sines — Tables  for  Earthwork, 
for  Setting  out  Curves,  and  for  various  Calculations,  etc.,  etc.,  etc. 

The  Chemistry  of  Sulphuric  Acid  Mamifacture.     By 

HENRY  ARTHUR  SMITH.     Cuts,  crown  8vo,  cloth,  4^.  6d. 

CONTENTS : 

Ground  Plan  of  Kilns  for  Burning  Sulphur  Ores— Section  of  Pyrites  Furnace— On  the 
Presence  of  Arsenic— Methods  for  Removal  of  Arsenic— An  Experimental  Examination  of  the 
Circumstances  which  determine  the  Action  of  the  Gases  in  the  Lead  Chamber— On  the  Dis- 
tribution of  Gases  in  the  Lead  Chamber— On  the  Temperature  at  which  Nitnc  Acid  acts  upon 
Sulphurous  Acid— On  the  Distribution  of  Heat  in  the  Lead  Chamber— An  Inquiry  into  the 
Best  Form  of  Leaden  Chamber,  etc. 


14  CATALOGUE  OF  SCIENTIFIC  BOOKS 


The  Principles  and  Practice  of  Engineering,  Trigono- 

metrical, Siibterrancozis,  and  Marine  Surveying.  By  CHARLES  BOURNE, 
C.E.  Third  edition,  numerous  plates  and  woodcuts,  8vo,  cloth,  5-r. 

Table  of  Logarithms  of  the  Natural  Numbers,  from 

i  to  108,000.  By  CHARLES  BABBAGE,  Esq.,  M.A.  Stereotyped  edition, 
royal  8vo,  cloth,  7-r.  6d. 

To  ensure  the  correctness  of  these  Tables  of  Logarithms,  they  were  compared  with  Callett's, 
Vega's,  Mutton's,  Briggs',  Gardiner's,  and  Taylor's  Tables  of  Logarithms,  and  carefully  read 
by  nine  different  readers  ;  and  further,  to  remove  any  possibility  of  an  error  remaining,  the 
stereotyped  sheets  were  hung  up  in  the  Hall  at  Cambridge  University,  and  a  reward  offered 
to  anyone  who  could  find  an  inaccuracy.  So  correct  are  these  Tables,  that  since  their  first 
issue  in  1827  no  error  has  been  discovered. 

BARLOW'S    Tables  of  Squares,  Cubes,   Square  Roots, 

Cube  Roots,  Reciprocals  of  all  Integer  Numbers  up  to  10,000.  Post  8vo, 
cloth,  6s. 

CAMUS  (M,)  Treatise  on  the  Teeth  of  Wheels,  demon- 

strating the  best  forms  which  can  be  given  to  them  for  the  purposes  of 
Machinery,  such  as  Mill-work  and  Clock-work,  and  the  art  of  finding 
their  numbers,  translated  from  the  French.  Third  edition,  carefully  revised 
;and  enlarged,  with  details  of  the  present  practice  of  Millwrights,  Engine 
Makers,  and  other  Machinists.  By  ISAAC  HAWKINS.  Illustrated  by 
i$  plates,  8vo,  cloth,  5*. 

The  Practical  Sugar  Planter;  a  complete  account 

,of  the  Cultivation  and  Manufacture  of  the  Sugar  Cane,  according  to  the 
latest  and  most  approved  processes,  describing  and  comparing  the  different 
systems  pursued  in  the  East  and  West  Indies  and  the  Straits  of  Malacca, 
adjid  .the  relative  expenses  and  advantages  attendant  upon  each,  being  the 
result  of  sixteen  years'  experience  as  a  Sugar  Planter  in  those  Countries. 
By  LEONARD  WRAY,  Esq.  8vo,  cloth,  ios.  6d. 

Laying  and  Repairing  Electric  Telegraph  Cables.    By 

Capt.   V.    HOSKKER,    Royal   Danish   Engineers.       Crown  8vo,    cloth, 


The  Practice  of  Hand  Turning  in  Wood,  Ivory,  Shell, 

etc^,  with  Instructions  for  Turning  such  Work  in  Metal  as  may  be  required 
in  .the  Practice  of  Turning  in  Wood,  Ivory,  etc.,  also  an  Appendix  on 
'Ornamental  Turning.  By  FRANCIS  C  AMPIN.  Second  edition,  -with  wood 
engravings^  ,crowji  .8vo,  cloth  (a  book  for  beginners),  6s. 

CONTENTS  : 

On  Lathes~-Turning  Tools—Turning  Wood  —  Drilling  —  Screw  Cutting  —  Miscellaneous 
Apparatus  and  Processes—Turning  Particular  Forms  —  Staining  —  Polishing  —  Spinning  Metals 
-—•Materials—  Ornamental  Turning,  etc. 


PUBLISHED  BY  E.  &  F.  N.  SPON.  15 


Health  and  Comfort  in  House  Building,  or  Ventila- 
tion -with  Warm  Air  by  Self-Acting  Suction  Ptrzver,  with  Review  of  the 
mode  of  Calculating  the  Draught  in  Hot- Air  Flues,  and  with  some  actual 
Experiments.  By  J.  DRYSDALE,  M.D.,  and  J.  \V.  HAYWARD,  M.D. 
Second  edition,  with  Supplement,  demy  8vo,  with  plates,  cloth,  Js.  6</.j 
the  Supplement  separate,  6d. 

Treatise  on   Valve-Gears,  with  special  consideration 

of  the*  Link-Motions  of  Locomotive  Engines.     By  Dr.  GUSTAV  ZEUNER. 
Third  edition,  revised  and  enlarged,  translated  from  the  German,  with  the 
.special  permission  of  the  author,   by  MORITZ   MULLER.      Plates,  8vo, 
'* cloth,  I2J.  6d. 

Treatise  on  Watchwork,  Past  and  Present.     By  the 

Rev.  H.  L.  NELTHROPP,  M.A.,  F.SA.  Numerous  illustrations,  crown 
8vo,  cloth,  6s.  6d.  CONTENTS  : 

Definitions  of  Words  and  Terms  used  in  Watchwork— Tools— Time— Historical  Sum- 
mary— On  Calculations  of  the  Numbers  for  Wheels  and  Pinions;  their  Proportional  Sizes, 
Trains,  etc.— Of  Dial  Wheels,  or  Motion  Work— Length  of  Time  of  Going  witKbut  Winding 
up— The  Verge— The  Horizontal— The  Duplex— The  Lever— The  Chronometer— Repeating 
Watches— Keyless  Watches — The  Pendulum,  or  Spiral  Spring — Compensation — Jewelling  of 
Pivot  Holes— Clerkenwell — Fallacies  of  the  Trade— Incapacity  of  Workmen— How  to  Choose 
and  Use  a  Watch,  etc. 

The  Present  Practice  of  Sinking  and  Boring  Wells, 

with  Geological  Considerations  and  Examples  of  Wells.  By  ERNEST 
SPON,  Member  of  the  Society  of  Engineers,  of  the  Franklin  Institute,  of 
the  Iron  and  Steel  Institute,  and  of  the  Geologists'  Association.  Crown  8vo, 
cloth,  illustrated  by  276  diagrams  and  engravings  to  scale,  "js.  6d. 

Workshop  Receipts  for  Manufacturers,    Mechanics, 

and  Scientific  Amateurs.  By  ERNEST  SPON.  With  numerous  illustrations, 
45°  PP->  crown  8vo,  cloth,  5-r. 

CONTAINING  RECEIPTS  FOR 

Bookbinding — Bronzes  and  Bronzing— Candles — Cement — Cleaning — Colour-washing — 
Concretes — Dipping  Acids — Drawing  Office  Details — Drying  Oils — Dyeing — Dynamite — 
Electro-Metallurgy  (Cleaning,  Dipping,  Scratch-brushing,  Batteries,  Baths,  and  Deposits  of 


ounry  xures — reezng — umnates — urnure  reams,  s,  oses,  acquers,  an 
Pastes — Gilding — Glass  Cutting,  Cleaning,  Frosting,  Drilling,  Darkening,  Bending.  Staining, 
and  Painting — Glass  Making— Glues — Gold — Graining — Gums — Gun  Cotton — Gunpowder- 
Horn  Working — Indiarubber — Ink  (Writing  and  Printing) — Japans,  Japanning,  and  kindred 
processes— Lacquers — Lathing— Leather— Lubricants— Marble  Working— Matches— Mortars 
— Nitro-Glycerine — Oils — Paper — Paper  Hanging — Painting  in  Oils,  in  Water  Colours,  as 
well  as  Fresco,  House,  Transparency,  Sign,  and  Carriage  Painting — Photography — Pig- 
ments— Plastering — Polishes — Pottery  (Clays,  Bodies,  Glazes,  Colours,  Oils,  Stains,  Fluxes, 
Enamels,  and  Lustres) — Scouring — Silvering — Soap— Solders — Tanning — Taxidermy — Tem- 
pering Metals — Treating  Horn,  Mother-o'Pearl,  and  like  substances — Varnishes,  Manufacture 
and  Use  of —  Veneering  —  Washing  —  Waterproofing  —Welding  —  Whitewashing.  —  Besides 
Receipts  relating  to  the  lesser  Technological  matters  and  processes,  such  as  the  Manufacture 
and  Use  of  Stencil  Plates,  Blacking,  Crayons,  Paste,  Putty,  Wax,  Size,  Alloys,  Catgut,  Tun- 
bridge  Ware,  Picture  Frame  and  Architectural  Mouldings,  Compos,  Cameos,  and  others  too 
numerous  to  mention. 


1 6  PUBLISHED  BY  E.  &  F.  N.  SPON. 


THE   TRANSACTIONS   OF   THE    SOCIETY   OF 
ENGINEERS. 

Published  Annually.     8vo,  cloth,  price  15^. 

THE    JOURNAL    OF    THE    IRON    AND    STEEL 
INSTITUTE. 

Published  Half-yearly.     8vo,  sewed,  price  Js.  6d. 

THE  JOURNAL  OF  THE  SOCIETY  OF  TELEGR^f  H 
ENGINEERS. 

Published  Quarterly.     8vo,  sewed,  price  fs.  6d. 

THE  PKOOEEDINaS  OF  THE   ASSOCIATION   OP   SANITARY 
AND  MUNICIPAL  ENGINEERS  AND  SURVEYORS. 

Published  Annually.     8vo,  cloth,  price  los.  6</, 

NOW  IN  COURSE   OF  PUBLICATION. 

To  be  completed  in  about  30  Monthly  Parts,  each  Part  containing  64  pp., 
with  mimeroits  illustrations^  super-royal  8vo,  price  2s. 

SPONS'  ENCYCLOPEDIA 

OF  THE 

INDUSTRIAL   ARTS,  MANUFACTURES,  AND   COMMERCIAL 

PRODUCTS. 
EDITED  BY  GEO.  G.  ANDRE,  F.G.S.,  Assoc.  INST.  C.E. 


NOW  IN  COURSE   OF  PUBLICATION. 

To  be  completed  in  about  15  Monthly  Parts,  each  Part  containing  64  pp., 
with  numerous  illustrations,  super-royal  8vo,  price  2s. 

A  SUPPLEMENT 

TO 

SPONS1  DICTIONARY  OF  ENGINEERING, 

CIVIL,   MECHANICAL,   MILITARY,   AND   NAVAL. 
EDITED  BY  ERNEST  SPON,  MEMB.  Soc.  ENGINEERS. 


London:  E.  &  F.  N.  SPON,  46,  Charing  Cross. 
New  York :   446,  Broome  Street. 

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